I tend to be a bit guerrilla with patterns- sewing ones, to date! Though a major difference is that I'm quite a competent seamstress whereas I'm a bit of a newbie to knitting! I am thinking I'll knit my cardigan with double rib as, being 'a bigger lass' (16, with hips!) I don't need any cinching at the waist!
So you actually alternate 'knits' above 'purls' and vice versa.
The first row will be k2, p2, k2, p2 all along finishing with k2. The second row will be p2, k2, p2, k2 all along finishing with p2.
I'm currently knitting a baby cardigan in DK with double rib. The rib is knitted on 3.25mm and the main part is on 4mm but on the last rib row you have to decrease so that the main part is the same width as the rib IYSWIM. You would need to check the cardigan pattern for instructions.