We no longer have a club mobile phone - it has disappeared!!
The following rules are just a starting point. They are rules because in the majority of hands they give the best percentage chance of making the most tricks, but there are many exceptions to these rules.
If you win a trick and are in doubt as to what to lead next, try not to open up another suit. This is a recipe for disaster because it pinpoints for declarer where all the losers or problems lie. Always return partner's lead if you can. Make sure you have a strong discarding system with your partner. If you are playing with somebody who has no system, insist that they play one. There are several on the market.
Another useful point is to make a mental note of Declarer's shape from the bidding. Having done that, keep length with declarer if you have four cards in one of their suits. Likewise, if you see a 4-card suit in dummy and you have four cards in that suit, do not discard from that suit. If you do, sure as "eggs is eggs" you will give declarer an extra trick.
Best of luck.