Best for deep colour is St Tropez (but needs to be done night before - leaves you looking muddy till you wash off the top layer the next day - I find it too much hassle and only use it for special occasions when I can plan ahead).
For a medium colour and zero streaks try Elegant Touch Cool Crackle Self Tanner Instant Bronze, which you can buy on Amazon (my personal fave, only light colour, but can be built up in layers, has light instant colour and dries the fastest out of any self-tanners and doesn't have a horrible smell).
For a light tan that never streaks, Asda own brand Sun System is fab - less than �3 for a big tube and can be built up over a few days.
I've tried them all (I'm beauty editor on a paper) and find that irrespective of which you use, exfoliation is crucial - ignore the advice of the self-tan manufacturers, scrubs scrape the skin unevenly and give you streaky results (those shower puffs are even worse!). Best thing to exfoliate with is a good old-fashioned facecloth - scrubs your skin evenly for a good base.
I don't moisturise all over before tanning - I find this just makes the tan too pale - but slapping on loads on your elbows and around your knees, ankles and feet is vital to prevent tell-tale faketan patches (also give your elbows a wipe with a damp facecloth after applying fake tan).
And (finally!) always use thin rubber gloves to apply your tan so you don't have to worry about tanned palms (you can buy them in Boots or use the ones you get in a hair dying kit). Makes it easier to really rub in the fake tan (which is important for getting it even - rub it in like you would do with a body lotion). When you take them off, wash your hands then apply a dot of fake tan to the back of one hand and rub the backs of your hands together.
Good luck! God knows there's no other way to get a tan right now with this weather!