Hi
First, double of preempts should be for take-out. This includes not only 3D-DBL, but also 4S-DBL.
Now then, you will hear a lot about support for other suits and the like. For instance, most double 1C holding.
S-KQxxx
H-AJxx
D-Qxx
C-x
It has an opening hand, three card support or better for all suits, and an added bonus, at least four in both majors. I don't double 1C this hand. I overcall 1S. There are several reasons for this. It tells partner I have 5Spades, so he will know how high to compete with 3 card support. If the bidding goes either:
(1C)-1S-(2C)-P-(P)-?, or
(1C)-1S-(P)-P-(2C)-?
I can now double to show my shape (5S and support for both red suits). So I will bid my five card majors at the one level instead of doubling. Also, I bid reasonable 6 card minors up to the two level rather than doubling with distributions like 1-4-2-6 and 3-3-1-6 where the 1 is in their suit.
On the other hand, change the cards around a little and give me the same hand pattern and have opener bid 1S
S-x
H-KQxxx
D-AJxx
C-Qxx
(1S)-?
Now I would double, not bid 2H. The reason is my heart suit is not strong enough to risk a two level overcall.
If you don't have a copy of lawrence handy, a nice discussion of how to think about doubles (over opening bids and preempts) can be found in the early part of chapter 5 of the Robson/Segal book on partnership bidding. And the great thing is you can download it for free to your computer, read what they have to say about takeout doubles and see if it applies to you. The rest of the book is probably too deep for a beginner, so I was initially hesitant to suggest it to a thread for beginners, but the part specifically discussing takeout doubles (chapter five, subsection entitled "The take-out double - a commercial break!" starting on page 166 is for anyone. To download a free copy of theis out-of-print book in adobe pdf format, go to
http://www.geocities...neill_2000/sys/
Then scroll down to the link to "Robson/Segal notes" link under "more stuff". This file is zipped so you will need one of the pkunzip type programs to decompress it.