When the opponents open the bidding it can be difficult to join in the fun and bid. To overcall you should have a good suit - the more so if you are entering the fray at the two-level.
One way of getting involved is via a take-out Double. A Double of an opponent's bid says that you are short in that suit and you have support for the other three suits. It also says that you have the values to open the bidding... more or less.
The more suitable your hand is in terms of shape the more inclined you should be to enter the auction. Conversely, the less suitable your shape is the more inclined you should be to keep schtum.