This is my reply to a question on new suit game tries after 1S-2S:

It is best to always avoid jumping after the try, since these tries are often slam tries. To that point, I would suggest that one not make many game tries in a suit, and instead either jump to game (the try will be in trying to make it), or bid a non-descriptive 2NT as a general try - so sequences become like 1S-2S--2NT(general try)-4S(cool). My experience is that by keeping the opponents blind more than offsets not accurately determining if the game is good enough double dummy. I would not use two-way game tries, and would avoid sequences that become too trying, like 1S-2S--3C(try)-3H(try in return)--?

So 1S-2S--3 new suit is usually a slam try. However it can work as a game try too. What is important is to not jump in reply, to keep the bidding space. The key responses are:

3S: Don't like the try.

3NT: Got enough to accept a game try, and my values are in the other two suits.

Cheapest new suit bid: Artificial, waiting, more than a 3S bid. Now opener will cuebid with a slam try.

Raise of game try: If you play the try as natural/semi-natural (instead of help suit), then this is a hand that would accept the try, and has a 4 card or better fit.