Some things are obvious

• Get a better understanding with your partner what the various calls mean
• Discipline - don't bid unless you have something extra to say. Once you have said everything, it is up to partner to decide what to do (unless he forces you to bid again)
• Try and assess how many tricks your side and the opponents can make in the various contracts. A good rule here is the 'Law Of Total Tricks': generally the total number of tricks that can be made by both sides is equal to the total number of trumps of both sides added together: So if you have a 9-card fit, and the opponents also have a 9-card fit then the total number of tricks to be made is 18: So if they can make 4♥ (10) tricks, then you can make 8 tricks in your best suit.
• Pay attention to the bidding (or lack of it), signals and discards your partner and the opponents make (you can always ask at your turn to play what signals/ discards opponents make.
• Read books and practise to improve your card-playing technique