I suggest avoiding these, only if you are worried about points, or losing. If you just want to have fun, and challenge yourself, join away, just be realistic about your odds of winning.
Freestyle. If you do not have click maps, and if you do not know all the tricks, just avoid it for a while..or play one or two, but not too many
Big maps. Most of the big maps give veterans an advantage. There are more choices and therefore more chances to miss something. For veterans, the bigger the better, for the new player, the smaller the better, in general.
Technical or specialty maps Again, this is only if you care about winning or points. These maps are alot of fun, but the people who play them regularly have an unbelievable advantage on them. Examples are Mogul, Age of realms 1, 2 & 3, waterloo, etc. Always look at the map first before joining. If it looks complicated, either join expecting to lose, which is what I do, or simply join a less complicated one.
Team Games. If you dont know who youre partner is going to be, and you join a game with an established team and experienced players, there is little chance of winning. The bigger they get, the less likely your odds. Again, you have to learn sometime, but finding a consistent partner would be better place to start, than randomly hoping for one.
At some point you will love playing these maps, but the game is more easily understood on the more basic ones. Once you have some fun with those, the principles will apply to the bigger ones.