Kinect Sports

Ok, the easiest way of getting this achievement, along with the other level based achievements is to play the mini games.

To be able to get this as quick as possible you need to make sure you don't play any mini games, hence set any PBs.

Then you can play each mini game and set the lowest score possible, this will result in a pb and a very decent xp boost. Eg - play the table tennis rally mini game and score 1 then miss on purpose, then play again and score 2 and then miss, then 3, then 4..... Each time you will set a PB and get an xp boost.

Use this same method on all the other mini games and you will level up in no time.

Just remember not to go setting awesome PBs as you will find them hard to beat and not get as many xp boosts!

The quickest way is to play against champion difficult bot. When you win the game then you get more than half the level of each game. My easiest sport was beach volleyball and this might be best sport to do this because you only need score 7 points and if you know the technique then winning will be very easy. Continue this and you get the achievement quickly. This will take max. 90 game wins (almost 2 wins each level) depending what is your level when you start to pursue this achievement.

The other solutions tell you that beating your own PB's allow you to get XP, which is correct, but I thought I would share more information about this achievement, as well as the best game modes to quickly rack up PB's.

Basic Information For Starters
I would highly recommend going for the level achievements as early as you can, because you will have easier PB's you can set, if starting fresh you can purposely fail after 1,2,3, and so on until you get a PB that is too hard to top or will take too long to be efficient enough. Another solution stated that 2 players allows you to get more XP in addition to setting a PB. Now something that isn't mentioned anywhere that I looked, is that you actually get even more XP if you set the amount of players to 4, and beat those other players. Combining these strategies allows you to earn XP at around double the rate that you would just beating PB's. None of the solutions here on TA highlight mini games that are faster than others. This is very important, because there is no reason to waste your time on a mini game such as Target Kick, where you have to wait for the timer to run out. Below are the general strategies for each mode that is worth your time. If you can't top you PB on any of these modes before you reach level 50 you can just score 1 point with your main player to end the game faster, although you will get less XP, but this shouldn't be a problem by the time you reach that point.

Rally Tally
This is easily the best mini game for gaining XP, because as soon as you miss the ball, it's over. Then with the remaining players, keep your hand raised so that you don't accidentally hit the ball and score points. you can probably keep chaining PB's until the 20s or 30s, whatever you are comfortable with. Remember, there are other modes that are just as quick. You will probably end up around level 20-30 by the time you finish your PB's here.

Bump Bash
This mini game is also quite good, and doesn't take too much longer. Avoid the objects thrown at you until You set a PB, then get hit 3 times to lose your "lives". It should be relatively easy to get hit 3 times with the remaining players, because you can just reach your arms out if you are not standing where the ball is thrown. Same with this mode, chain PB's until the 20s or 30s. You should be at around level 30-40 by this point.

Super Saver
This one is real easy. Reach for the ball until you set a PB, and then hold still until you lose your "lives". Hold still with the other players and you should be good to go. At this point, you should be somewhere between level 40-50 if you are not done yet by this point.

Body Ball
Not as good as the last 3 mini games but still can be done really fast if you are almost at level 50 but need 1 last push. Your strategy is similar to Bump Bash, except you want to hit the ball until you reach a PB, and then avoid the ball until you lose your "lives". You may not get as much XP from PB's here, since it is easy to accidentally hit a ball, so you might want to score a few at the beginning.

Let me know if there are an modes that are more time efficient and anything else I can do to improve this guide.