Keep your conventions to a minimum, most of them come up very rarely. If you play with a particular partner often, and you feel the urge to explore, then add an occasional convention to your repertoire.
To start this adventure, I will suggest one convention.
For advanced players here is one that has some useful features:
In the absence of competition, your partner opens 1NT, you are an unpassed hand with no four card or longer major, but a desire to bid. Two spades by you asks partner if he has a minimum or maximum. Two notrump announces a minimum and 3 clubs a maximum. This is equivalent to 1 NT-2 NT invitational. Suppose that instead of a straight invitational hand, you have a weak hand with clubs. If after your two spade bid, partner bids 3 clubs, you pass. If he bids 2NT you correct to 3 clubs. If you have a strong hand with clubs, you can bid a new suit which is a cue bid or fragment or whatever continuation works best for your system. Note that if you are in an invitational sequence, the opener doesn’t have to tell the opponents which major he has, if any. This is the most common use of the convention by far and it is important to conceal declarer’s hand as much as possible.
Similarly if you have diamonds, bid 2NT over 1NT. Partner with a fit for diamonds, will bid 3 diamonds and without one bids 3 clubs (or the other way around, your preference). If you have a weak hand with diamonds either pass or correct to diamonds. With a stronger hand either bid 3NT or make some other bid. Note that in either case, that if partner makes a weak response and you continue on, you announce a strong hand with either a club suit (after 1NT-2 spades) or a diamond suit (after 1NT-2NT).
Other more sophisticated followups are possible, but in practice the opportunity to use them is very rare.