Not sure if it's been said already but for applying makeup
anywhere, apply a primer. You can get silicon-based and silicon-free ones, they're usually in small clear tubes and have a slight glossy tint. Smashbox do a great one that I swear by called "Photo Finish", but if you're on a budget GOSH do a pretty good dupe of it in Superdrug. There are also ones from Benefit, MAC, Bourjois, etc though - have a browse around and try a few! It evens out your face and fills your pores, meaning makeup goes on smoother. As long as you don't get anything with ingredients that are going to irritate your face, it's worthwhile investing as primers calm your skin and help makeup last, too.
As for actual products/application, I think that's been covered!
For your skin, do NOT apply makeup to your arms/legs unless totally required as it will only make the condition worse; for your legs, look into investing in some dance tights, or high denier tights at least. Dance tights are usually matte, which makes them look more natural, and they're usually thicker too.
Capezio are a great brand with a lot of different colours of opaque tights usually around £10, and they're excellent quality - I have really sensitive, blotchy legs but I've had a pair for about 3 years now and they're great. They're thick, but not uncomfortable, don't ladder badly and show nicely in photographs. The best place to get them cheap is probably Amazon:
http://www.amazon.co.uk/Capezio-Hold-Stretch-Footed-Tights/dp/B006TX8SC4
Hope that helps!