343 and 442 diamond are good formations to get used to the gameplay. Later on you can either stay with those or switch to 3223 or 4231.
If you want to use a different tactic for defending, means switching between tactics during the match, I'd recommend using 541 for learning how to defend. It isn't the best defense tactic out there but good for new people. Later on you can switch to 352, which is a bit harder to play.