Creating your game
When you first start a new game you must choose your database, if there has been a patch which updates the database you are best off choosing the latest version to have a more up to date game. If you have made any changes in the data editor you can view and select which editor files you want in your game by ticking the change button. Be careful with selecting more than one editor file as conflicts could cause issues.
After your finished with the database you have various options starting with which leagues you want active, the following screen give you various options such as how big a database you want, how many leagues and additional options such as attribute masking.
Select your leagues
Decide what leagues you want active in your game, this determines what teams you can manage and which leagues will be active and viewable. Active leagues have clubs which you can manage. A view only league can be viewed but the clubs cannot be managed. All players from active leagues are automatically included in your database size.
As an example I traditionally I use England(EPL - BSN/S), Scotland(SPL-D3), Italy(A-B), Spain(BBVA - Adelante ), France(Ligue 1-2), Germany(Bundesliga 1-2) and Holland(Eredivisie - Eerst Divisie). Depending on how I feel I sometimes add other leagues like Czech, Belgian and Portuguese because I like to see how the leagues develop and have the option of playing in them.
Database/loading players
You can decide how many players are loaded in your game in addition to your active leagues by changing the database size, you can also be more selective and load additional players from leagues and nations not previously selected by using a custom database as shown in the highlighted area in the screen above.
I usually load all players from each EU nation to give an overall player count of around 175000. Also consider loading all international players from each continent as these can easily get work permits despite being non-Eu.
More recently I have being loading far more leagues but no additional players to give me a final count of 49 leagues and 100,000 players, I've found this runs faster and gives me many leagues and players while excluding a number of very low reputation and ability players whose only use would be to slow down my games speed.

Advanced options
You can also choose some additional options on the new game overview screen:
- Attribute masking - hides player attributes that you are unlikely to know, these masked attributes can be revealed through scouting. Unticking this option makes all in game attributes viewable.
- Add Key staff - creates newgen staff for clubs without coaches, scouts, physios etc.
- Use Real players - will create known players from the real football world, unticking this option will create entirely new players similar to real world players.
PC performance
The number of players you load affects how quickly the game processes, with 10,000 players loaded it will run extremely quick whereas with 200,000 players loaded it will naturally take longer. My selection of leagues and 219,000 players runs at a speed I'm happy with on my laptop which has 3GB RAM and an Intel i3 2.3GHz processor, for slower computers you may need to keep the number of leagues and players lower.
It's worth knowing that the number of players loaded has a bigger affect on the game speed than the number of leagues loaded, for example a game with 5 leagues and 200,000 players will run slower than a game with 30 leagues and 100,000 players.
Your manager profile
When your game has been created you need to create a manager.
Your nationality will give your 100% knowledge of that countries staff and players, a secondary nationality will give you 50% knowledge of that countries staff and players.
Your reputation will determine how well respected you are, a low rep will mean that better players struggle to motivate themselves to play for you and also take less notice of what you say, players will be less likely to accept your tutoring and preferred move suggestions.
Your manager profile is basically a representation of how you manage your team, what is shown here does not affect anything in the game other than how you may be described by the media.
Discussion: FM12 Guide - Creating your game
5 comments have been posted so far.
One question I had:
You note under PC Performance that RAM is the main factor to be able to handle a big database. Though isn't your processor more important to reduce the time it takes to 'continue' the time in the game?
As I have 8 gb RAM, so if RAM is the main factor, I will start making much bigger databases