[keledor]

The answer to your question is to agree with your partner what the following bids show....

Double - Negative or just values (and how much!).
1NT - how many points does it show and does it promise a stop (if it doesnt your partner should alert...)
2♣/♦ - forcing or non-forcing and does it promise 5+cards?
2♥ - does it show values (or not) and how much support 3 or 4 cards for example?
2♠ - Forcing but what else does it show!

Now I tend to play the following and its pretty effective.

Double - values 8+pts and no better bid yet - I'll show more on my next bid...Partner should bid as they would if I had bid 1♥ or 1♠.
1NT 6-9pts and at least 1 stop.
2♣/♦ 5+cards and the same as if the opponent hadn't overcalled.
2♥ weak 0-5pts and 3+support
2♠ Forcing the same as 4th suit forcing - tell me more.