NBA 2K11

Easiest way to do this is to get someone to boost with. What you do is both change your time zone to something that would make it around 4am.

After that, you go to Ranked Game (found under Quick Game). Have one person search, and if there are no other matches, it will create one, then have the other search.

Once you're in the game, just have one person quit out. Repeat until this has been done 19 times each (you can check leaderboards to see how many wins you're at).

**EDIT** Apparently the wins don't show up on leaderboards for games where your partner quits out. Also from the comments, don't quit out until after tip-off.

For the 20th win, you have to finish the game.

At the end of the 20th win, you will get the achievement for 1 win, 3 game winning streak, 5 game winning streak, 5 wins, 10 wins and 20 wins (assuming you haven't already gotten them).

Assuming you don't have trouble matching up, this should take about 45 minutes or so for each of you to do.

I just want to clarify a few things here:

1. Changing your time zone does in no way guarantee that you and your boosting partner will get matched up. From my experience NBA 2K11 uses a server queue system. When you change your timezone, you are really just entering a different server queue.
a.) Being in a different server queue (i.e. region) does not mean that you cannot match up with people in your normal queue.
b.) It takes forever to find a game when set up as America, because there are many more people playing, therefore the server queues are much longer.
2. What time it is in the locale you are changing to makes no difference. (For reason see 1a and 1b).

As for how to get the achievements:
1. All party members change your TIMEZONE & your LOCALE. It shouldn't really matter which, as long as it is outside of North America, though my personal preference was Taiwan/Taipei.
2. One person goes to ranked match, on the away side (I am just passing on this tip from my partner and am not professing that this part is entirely true, nor can I explain why it works). Apparently since most people are on the Home side when they select ranked it adds them to the queue, however when you go away, since there is a lack of players there, it will create a match.
3. As soon as a match is created, the 2nd player begins searching.

This method worked for a friend and I to clean up about 15 games in less than an hour. An alternative, and more fun/efficient method is to set up a four person session, have everyone change time/locale and just search at random - rotate wins and keep them as even as possible - it will all go by very fast.

**If you are using this as a reference for boosting the Crew/Team-Up achievements let me stop you now! Put 2-3 players together and get it legit by toughing it out against the glitched 99 jerks. Getting two teams matched in Crew is nigh-on impossible, and even if you do its likely that all teammates but the captain will glitch out. (I've spent well over 10 hours in multiple sessions trying to matchup. Even with 12 people spread over 6 teams we only had 2 matchups in 3 hours, and they both glitched out with only one person total getting the achievement.)**

Please let me know if there is anything additional you feel I should add or change in the comments.

I will begin this by saying that I have no qualms with boosting and I think the 2 guides already posted are excellent for those attempting to boost. Me personally, I got frustrated trying to boost this game as I could never get matched with anyone. I went for this and the streak achievements normal, and this guide contains tips for anyone else going for this without boosting:

First, most people online use the "power" teams. By that I mean you will almost always play against the Heat or the Lakers and occasionally the Celtics. A great team against all of these is the Thunder. I got all my wins using them and I was blowing people out without having to adjust the settings too much.

Tips while using the Thunder:

-Don't jack up shots with Durant nor try to drive all game with Durant. My opponents would usually forget about him by halftime and I could find him alone on the perimeter for a wide open shot. This is his strength.
-Use the 1-3-1 defense! This stops so many people online it almost isn't fair. People using the Heat/Lakers try to drive against you all game, and this defense stops them. Plus, when you get the rebound or steal (and you will get a lot of steals with this on interior passes), you have Westbrook and Hardin out on the break for easy lay-ups.
-Speaking of which, swap out Hardin for Sefalosha in the starting line-up. I turned subs on manual/fatigue and never had problems. Yes, Sefalosha is a better perimeter shooter, but you shouldn't be depending on 3's to win.
-Get Westbrook hot early with some of those fast-break lay-ups and he is unstoppable driving the lane later in half-court sets.
-Most offense possesions went like this for me: back down the defender with Westbrook near the top of the key (hold both triggers to do this). The CPU does a good job of automatically cutting to the basket when you do this. Your opponent is most likely playing on-ball, so it becomes sinfully easy to just toss a pass to a wide open man for a lay-up.
-I very rarely played on-ball defense, instead playing one of the wing players to deny passing lanes. People online abuse isomotion and they will get by you if you're controlling the defender. Plus, they would normally be expecting me to be controlling on-ball, so it would throw them off when they couldn't just dribble past the CPU defender!
-Last tip and probably the most important: play with the 2K camera from Myplayer! It takes a bit of getting used to, but once you are used to it you'll be unstoppable. I think it is much easier to play defense in this angle as you can see those passing lanes clearly.

That is pretty much it, just expect to put some time in if you're going for this legit. By using these tips, I quickly got to where I was blowing out almost every opponent by 15 or more and was getting alleys on many plays. I'm not crazy good at the game either, and struggled for like 20 games using the power teams before I switched to the Thunder, then got like 15 wins in a day or 2. Have fun!