99 overall player - Use the following trick to get your player up to 99 overall a lot faster. Before you start, make sure that the player you want to upgrade is your arena player.

Save enough points to buy all the experience packs in the shop. This should not take too long.

Once you have enough, save it onto a second personal settings as well as your first.

Buy all the experience packs in the shop, and save as normal. It should save to personal settings 2 and your squads. Use all the experience points on your chosen player.

Save the game as normal.
Load personal settings 1.
Save it to personal settings 2 again.

The experience packs should now be available in the shop again, and you should have your points back.. Buy them again and save as normal. It should save to personal settings 2 and squads as before.

Use all the packs on your player again.
Save as normal.

Repeat steps 6 through 11 to keep increasing your player's stats until he reaches 99 overall. Once your player is 99 overall, save and load personal settings 1.

Save it to personal settings 2.
Load personal settings 1 again.

Your chosen player will have 99 overall, you will still have all the points you had before to spend on whatever desired, and have personal settings 2 to use in case you want to do this again.

Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Genesis (10 points): As the lead profile, create a player.
Online First (10 points): As the lead profile in a single player game, win an Xbox LIVE ranked Match.
Tournament Creation (20 points): As the lead profile in a single player game, create a tournament.
English League (10 points): As the lead profile in a single player game, win the Barclays Premier League in Manager Mode.
German League (10 points): As the lead profile in a single player game, win the Bundesliga in Manager Mode.
Italian League (10 points): As the lead profile in a single player game, win Serie A in Manager Mode.
French League (10 points): As the lead profile in a single player game, win League 1 Orange in Manager Mode.
Dutch League (10 points): As the lead profile in a single player game, win the Dutch Eredivisie in Manager Mode.
US League (10 points): As the lead profile in a single player game, win the MLS in Manager Mode.
Spanish League (10 points): As the lead profile in a single player game, win the Spanish Primera in Manager Mode.
Grass Roots (5 points): As the lead profile in a single player game, win an Amateur game vs. the CPU.
Part Time Player (10 points): As the lead profile in a single player game, win a Semi-Professional game vs. the CPU.
Professional Footballer (20 points): As the lead profile in a single player game, win a Professional game vs. the CPU.
World Class Player (30 points): As the lead profile in a single player game, win a World Class game vs. the CPU.
The Legend (45 points): As the lead profile in a single player game, win a Legendary game vs. the CPU.
Defensive Hero (10 points): As the lead profile in a single player game, win Man of the Match as a Defender on World Class.
Midfield Maestro (10 points): As the lead profile in a single player game, win Man of the Match as a Midfielder on World Class.
Poacher (10 points): As the lead profile in a single player game, win Man of the Match as a Forward on World Class.
Real World (10 points): As the lead profile, Play an Online Interactive Leagues game to completion .
World Class Finisher (30 points): As the lead profile in a single player game, score more than 5 goals on World Class.
5 game streak (10 points): As the lead profile in a single player game, have a 5 game winning streak on Professional.
Single Player Hero (10 points): As the lead profile in a single player game, achieve a 90 player rating in Be a Pro.
50 game streak (40 points): As the lead profile in a single player game, win 50 games on Professional.
10 scored (50 points): As the lead profile in a single player game, get 10 or more goals in one match on Professional.
10 up (10 points): As the lead profile in a single player game, win 10 Xbox LIVE ranked matches.
Getting Serious (20 points): As the lead profile in a single player game, win 50 Xbox LIVE ranked matches.
Worldwide Legend (60 points): As the lead profile in a single player game, win 100 Xbox LIVE ranked matches.
Blank sheet (30 points): As the lead profile in a single player game, keep a clean sheet on World Class difficulty.
Host (10 points): As the lead profile in a single player game, host 10 Xbox LIVE Matches.
This is too much (40 points): As the lead profile, in a single player game host 50 Xbox LIVE Matches.
Boot Cleaner (15 points): As the lead profile, Complete Challenge Mode Region 1.
Youth Teamer (15 points): As the lead profile, Complete Challenge Mode Region 2.
Reserve (15 points): As the lead profile, Complete Challenge Mode Region 3.
Substitute (20 points): As the lead profile, Complete Challenge Mode Region 4.
First Team Debut (20 points): As the lead profile, Complete Challenge Mode Region 5.
First Team Regular (25 points): As the lead profile, Complete Challenge Mode Region 6.
Man of the Match (25 points): As the lead profile, Complete Challenge Mode Region 7.
Captain (30 points): As the lead profile, Complete Challenge Mode Region 8.
Veteran (30 points): As the lead profile, Complete Challenge Mode Region 9.
Football Legend (95 points): As the lead profile, Complete Challenge Mode Region 10.

Additionally, there are nine secret achievements:

Scruffysocks Scores (20 points): In a single player game, score a Hat Trick with a created player.
Competition Winner (20 points): Win a Created tournament.
World Wide Hat Trick (20 points): In a single player game, score a Hat Trick in a ranked Xbox LIVE match.
Extra Bonus (20 points): In a single player game, wins by 2 goals in Extra Time on World.
Beat Yourself (0 points): In a single player game, score two own goals in a single game.
They Drew A Blank (20 points): In a single player game, keep a clean sheet in an Xbox LIVE ranked match.
Lightning Finisher (10 points): As the lead profile in a ranked match online, score a goal in under 5 minutes.
Tour Bus (20 points): As the lead profile, play in every stadium in the game.
Manager Merry-Go-Round (10 points): As the lead profile, play 15 years for 15 different clubs in 15 different countries.