I use the best quality gouache paints possible on thick, acid-free watercolour paper with a smooth surface. The Winsor and Newton gouache range is good. Their website has tips on gouache technique. Here's a link: www.winsornewton.com
Some artists report that M. Graham and Schminke artist’s gouache are the very best to paint with, and are not too much more expensive than W&N. You might have to mail order these brands. I have yet to try these, but probably will soon, and I'll try to review them in a post.
Gouache paints vary in opacity and drying time. I have had problems with certain white cheap gouache paints remaining sticky for a long period. Because most gouache colours dry very quickly, you can get caught off guard and ruin a painting by transferring the tacky paint on your hand.Gouache and watercolour are thinned with water, which tends to cause the paper support to buckle. Painting in fine detail on a bumpy surface is not ideal so I generally stretch the watercolour paper by wetting it and taping or pinning it to a board. As the paper dries, it becomes taut, and buckling is greatly reduced. The thicker the paper, the less this is a problem. Historically, paper for miniatures was sealed, presumably with some kind of gum arabic mixed with white, and this would have prevented water from the paints distorting the paper. Buckled paintings can be flattened under heavy books, once they have dried, although a severely buckled piece of paper can get creased in an attempt to flatten out the bumps. If a totally stable surface is desired, a stiff support such as illustration board is an option.