A lot of people ask me for help with booster drafting. I wish so badly it were the kind of thing where I could take 20 minutes of my time to listen to how they draft, tell them what they are doing wrong, and how to fix it. It just isn't. Booster drafting well is incredibly complex.
The best way I can describe it is that there are two ways: The easy way and the hard way. If you draft the easy way all the time, you can spike when things line up your way and you are perfectly live to 3-0 and draft good decks when they do, but around half the time you will not end up with a good deck at all and will be liable to 0-3 or 1-2 your draft. If you draft the hard way you can have a good deck in 90% of your drafts. Sound great? What's the problem? Well the hard way, is hard.
Drafting the hard way means analyzing each new format and being willing to forget about whether you like control or beat down, white or black. Forgetting about what was working for you in the last format and starting to evaluate everything from scratch all over again. Always being willing to drop early picks if you realize something else is open. It means not sticking to the strategy or strategies that you think are best but weighting the cards that are important for those correctly, and then still being willing to draft completely different decks if that's what is open.
It requires allowing your decks to go different directions in each draft and not predetermining where you are going to go. Every draft format is different and every draft is different. I don't even like doing our house practice drafts, because they bias me into thinking you should go certain directions more than you should, because certain strategies are either open or would work well against what the others in the group are doing. I generally prefer these days to watch the draft so that I don't get as caught up in trying to win. Instead I spend more time watching how the commons interact with each other and trying to pick up on how the games and format plays out.
Different things are a little more or a little less important in each new format. So at the start of a new format, I'm mostly trying to identify whether flying is a little better (Return to Ravnica). How about lifelink? (Zendikar). Is this a format where drawing cards is a little bit more profitable than usual (Modern Masters)? Or is this a format where a lower mana cost is of extra value (Gatecrash).
Let's look at a good example of this. I remember when we started our testing for PT Avacyn Restored, most people thought [card]Seraph of Dawn[/card] was better than [card]Mist Raven[/card]. It's not hard to see how this happened. In an aggressive format, the 2/4 would be much better. In a format where the cheap cards were more powerful, the 2/4 would be much better. Avacyn Restored was neither of those things, but the format directly before, Innistrad-Dark Ascension, was both.
A format where the cheap cards like Werewolves and [card]Travel Preparations[/card] hit hard and prevented late games, or were still good in the late game. In that format, the 2/4 would have been better than [card]Mist Raven[/card]. However, in Avacyn, the cheap cards were horrible. Games were mostly decided by individual powerful cards. The tempo swing from being able to bounce a soulbond that was preventing you from attacking or bouncing their powerful 5+ mana card that they were depending on to swing the game was extremely valuable. The 2 life a turn that makes it almost impossible to race the 2/4 was not particularly amazing, since you weren't usually racing. The 2/4 is still a good card, and one that could help you win games, but it was not the bomb it would have been in formats like Innistrad/Dark Ascension, Zendikar, or Gatecrash.
The single thing people do that ruins most drafts is stick to their early picks. In the vast majority of draft formats, you should be trying to figure out what is underdrafted at the table so that you can have access to a lot of what you are looking for in packs 2 and 3. Also, by identifying which colors/archetypes the people to your right aren't playing, you end up having several packs to get incredibly powerful picks from. Where as if you stick to your first picks, you often end up with very few packs to select first-pick quality cards from.
People often think that they can just jam what they want, because if they are cutting something off then they will have access to the cards that they want in pack 2 even if not in pack 3. This only works when pack 2 is specifically more valuable than pack 3. Even if you draft mono-white from pick 1, there were probably a few other white cards in the packs, and if the guy to your left or to his left is drafting in easy mode (95% of people are) and he opened or got passed a white card from the person passing to him (if it's the guy 2 seats down), then they are probably still going to draft white despite you not passing them any great cards in that color.
On the other hand, if you get a first-pick quality white card pick 4, and a 2-4th pick quality blue card pick 8, while nothing is guaranteed, you can bet your ass the vast majority of the time that the people to your right aren't drafting white and blue is heavily underdrafted at the table. The exception to this rule are formats where pack 2 is of disproportionately greater importance to you than pack 3.
A perfect example of this is DGR if you start out in a Gatecrash guild. Since you don't care much about pack 3, and pack 2 is your entire world, if your first 2 picks put you into a specific Gatecrash guild, you can just jam that guild and not bother to read what the people passing to you are playing ,or what is being underdrafted in the pod, since you basically live and die by only pack 2, and you are only looking for strong cards out of the first few picks of pack 2. Draft formats where this is correct like DGR are few and far between though.
The next thing that often ruins drafts is trying to draft the nuts or the best deck. Going for a combo or cards without synergy that don't fit their deck's plan, or are difficult to cast but have a high power level. I have 3-0'd so many draft pods with very mediocre looking decks. You don't need to be in the best color or archetype, you don't need a way to win, you don't even need particularly powerful cards to win. If your deck is fully functional, meaning the cards you do have work together, your curve is good for the format, and your mana allows you to cast your spells when you need to cast them (some formats you are under more pressure (Gatecrash), some you have a little more time [Rise of Eldrazi]), that is good enough to allow you to 3-0 any pod. Sure you won't have the best deck in the pod, but that's not how Magic works.
The most common scenario is not that you have the third best deck, and you play against the best or 2nd best deck you lose, otherwise you win. In that case, drafting the 2nd-3rd best deck in the pod every time would result in 2-1 every time. In reality, when you have the third best deck and you play against the best deck in the pod, you are usually just a small underdog because your deck is very good anyways. In general I feel outmatched when I play my 2-0 match in my draft pods, but assuming roughly even playskill I win that match around 45% of the time, because I have a good, fully functional deck. If he stumbles, gets flooded, or my cards just happen to line up well against his, I can very easily win. When you have good, fully functional draft decks, it is very easy to beat a better deck. When you have trainwrecks/bad draft decks it is very difficult to beat anyone.
A good example of this approach would be my first draft in PT Gatecrash. It was covered in the draft viewer so you can go back and check it out. I started out with some Orzhov stuff (the guild I consider the best by miles in triple-Gatecrash), but I wasn't seeing Orzhov, so around pick 5, pack 1 I realized Simic was open and completely jumped ship. I was very fortunate to have this opportunity. I had it because a lot of the other players in the draft were unwilling to draft Simic, because they thought it was the worst of the 5 guilds (Personally I think it was the 4th of the 5 guilds and not particularly good, but that Dimir was the worst). This unbalance allowed good Simic cards to come late, telling me that Simic was wide open and I jumped ship, drafted a mediocre Simic deck, and went 2-1.
If I had stuck to Orzhov, my deck would have been absolutely terrible, and while I have no idea what my record would have been, my EV in wins in the draft would have been much lower. I obviously was very unhappy to have to move from the best guild in the format to the 4th best guild out of 5, but you don't want to dictate what you draft, you want to draft what you see and what is being underrated. Any fully functional, reasonable draft deck, can 2-1 or 3-0 a pod. Trainwrecks struggle to get a win.
It took many years of endless drafting for me to improve my draft game and I've spent many years trying to slowly improve the drafting skill of many of my closest friends. If you are willing to play the game in hard mode, don't expect to be good at it quickly or to immediately start crushing. However, if you are willing to read every draft, be open to drafting whatever archetype is available that draft, and even drop bomb-rare first picks, you can put together a good draft deck in almost every draft you do and you can be a highly successful booster drafter. Will you accept this challenge? The choice is yours.