We have to be clear as defenders, that a suit contract play is very different to a no trump contract. We shall play much more passive defence, because declarer has much more opportunities to control the game. Let's see, how it works?
The most important of these differences is, that in notrump contracts there is race in developing long suits, so active defence needs to be played, whereas in suit contracts the declarer can control the suit establishing attempts of the devenders with his trump suit. So in suit contracts the opponents play a passive defence more frequently.
The main concept of passive defending is leading suit which does not give tricks to the declarer. One way of doing that is by leading closed suits (for example QJ10x), this is a double weapon, because a good sequence works for us and doesn't help declarer, but it is a rare combination. another is leading a neutral suit, which is almost always available. For example we can lead a suit of xxxxx several times, because if our partner has an honour, he can freely finesse (seeing the cards in dummy) as in such manouvres we always lead from small cards towards an honour anyway, if he has no honour at all, then all honours are on the declaring line, so we will not give a trick away by leading this suit.
Another difference between suit and notrump contract is that in suit contracts the third round of a suit rarely stands up, only if the suit is divided 4-3-3-3. This is only 8% of all cases, so it is better to concentrate primarily taking the first, then taking the second trick in the side suits! So, if we can take the first trick without giving a trick to the opponents, then take it!
In suit contracts the first trick is most important for both defenders, then the second, the defence can only rarely take the third trick in a side suit, while in notrump contracts in the long suit the defender is trying to develop the third trick is most important, then the second, then the first. On the other hand his partner forces declarer by playing his highest cards in the first and second trick, leaving his lowest to the end, so his partner could take the third round and continue the suit! (See „control of the third trick in a suit”)