The Rule of Eight
A handy tool for helping you get into the bidding over weak two-bids is known as the Rule of Eight.
Here's how it works. When your RHO opens with a weak two-bid, figure that your partner will have, on average, about 8 high-card points scattered through his hand. If you think that partner's 8 HCP will be enough for you to have a shot at whatever you are considering bidding, go ahead and take the plunge. If you need substantially more help than the average hand partner will provide for you, look again at your thirteen cards and reconsider your decision to get involved.
If you and your partner are in accord about the use of the Rule of Eight, be sure to apply it when it is your turn to bid after partner overcalls. When your partner bids over a two-level opener, be aware that he is counting on you for about 8 HCP. If that's all you have, it's best not to raise partner's bid, even with trump support. If you have good trumps and 9 or 10 support points, you can raise.
The Rule of Eight has other applications. Say dealer opens a weak 2 ♥. If you now bid 3 ♠, that is a strong bid, not a weak one. You don't pre-empt over pre-empts. Just as with a two-level bid, the overcaller is counting on her partner for about 8 support points. The difference is that when the over-caller bids 3 ♠ instead of 2 ♠, she is saying to partner, “I'm counting on you for 8 support points. If you have them, put me in game if we have a fit in spades — or do something else intelligent. If you don't have the points or we don't have a good spade fit, pass.”
The Rule of Eight loses its effectiveness when the opponents are opening the bidding at the three level and higher, so be a bit more careful when you have to start at higher levels.
When you overcall at the two level or higher, it generally shows at least a good suit. You are not always blessed with extra length or good intermediate cards in a hand that cries out for some action. For example, say an opponent opens 2 ♥ in front of you and you hold this hand:
You have a ratty spade suit, but you have a good hand with prime cards (aces and kings). You can't overcall in no-trump because you don't have hearts stopped and you don't have the high-card strength anyway. A takeout double is out because you can't support diamonds and if you bid 3 ♠ over 3 ♦, it shows a much stronger hand than you have (not to mention a much stronger suit). Passing is a very wimpy action. Yes, you could get nailed if opener's partner has a big spade stack behind you and some high-card points, but partner could also have those spades and HCP, so passing might let the opponents steal your game from you.
You might be a bit uncomfortable bidding 2 ♠ with this hand, but you have to do it.
Be sure, however, that if your suit is not of the best quality or length that you have compensating values. Translation: It's okay to overcall a somewhat ratty suit if your hand is pretty good and passing doesn't feel like a reasonable option.
The bottom line is that when the opponents are taking up your bidding space, you will have to make some compromises.