The first thing on which to agree is exactly what types of hand partner will hold when they double on the first round of bidding.  Imagine that right hand opponent opens one spade. Which of these hands do you think are suitable for a takeout double:

(i)    ª6 ©A643 ¨QJ75 §AK32.
(ii)   ª62 ©K9643 ¨KQ7 §AK3.
(iii)   ª62 ©AQ4 ¨AQ76 §AT63.
(iv)   ª62 ©A643 ¨AQ762 §K3.
(v)    ª62 ©A643 ¨K3 §AK762.
(vi)   ª63 ©A6 ¨AKQ7654 §A3.

All of these hands might be suitable depending on what you agree with your partner. Hand (i) is a classic takeout double, with a 4 card fit for anything partner cares to bid. Hand (ii) is less than classic, but the poor heart suit might make you circumspect about a two heart overcall, especially if vulnerable. One advantage of double here over the heart bid here is that you are not directing partner towards a potentially poor lead. Hand (iii) has more or less the right shape for a takeout double, but you have only three card support for the other major suit. Some partnerships are uncomforatble with this, although to me, it seems unnecessarily restrictive to actually promise four cards in the unbid major. Its one of those situations where it is better to have four cards but if you are not dealt them, what are you supposed to do. Its a bit  like those rare situations when I am laying down my hand and dummy and partner says something like " What went wrong - thats exactly what I expected  you to have from the bidding" - sometimes you are dealt the right hand, sometimes you are not; but my motto is "don't let a detail like that stop you from bidding".

Hand (iv) is not suitable for a double in some ways because it is not "SHAPE SUITABLE", you cannot support every other suit- for example what happens if partner bids two clubs. Some players would still double with this hand, hoping that partner would get the message if they correct two clubs to two diamonds. That is all very well if you have agreed this "same level correction",  but some sequences can get confusing. what if partner goes three clubs for example - or five clubs. Clearly hand (v) would be riskiers still sinec you cannot correct at the same level if partner bids the wrong suit.  My advice is to stick with shape suitable doubles unless you have a very strong flat hand or a very good one suited hand (GOSH) like hand (vi). With hands like this, you often have to start off with a double because you are too strong for a jump overcall, especially if you are playing weak jump overcalls.

OK, What happens next? Lets imagine that you have doubled one heart, next hand passes and partner bids one spade. Original opener passes and you have another chance to bid. Bearing in mind that partner might have very little (indeed they may have even bid one spade on a three card suit), how many have you have discussed with your regular partner what it means if you: a) bid a new suit b) raise c) jump in  a new suit d) cue bid the opponent's suit?
 
 

NORTH	EAST	SOUTH	WEST
	Pass	1 heart	Double
Pass	One Spade	Pass	????

It many ways it does not matter what you play now as long as partner knows what you have. For what it is worth my suggestions are:

2C/D:    Natural, Good suit:  This combines game try in spades with an unwillingness to play in a silly 3-3 fit or 4-3 fit
             For example:        ªKQ62  ©6 ¨AKJ96 §KT7.

2H:        Serious try but with only three spades
             For example:        ªKQ6 ©6 ¨AK76 § AK32.

2S:       Purely competitive, making sure that next hand does not reopen.
            For example:         ªKQ63 ©6 ¨AT74 §K765.

3C/D   GOSH.  Like an Acol two in that suit.

3S       Serious game try but with no good side suit:
            For example:         ªAQ63 ©4 ¨AQ74 §AK53.

If you have other agreements in these situations, please let me know.  Happy doubling!!