1: always exfoliate!! this is very important as this removes all dead skin which could case streaks. i advise to use some exfoliating gloves and just a shower gel will do the trick but if you would like to get an exfoliating body wash go ahead :)
2: moisturize specific try spots like elbows, knees the crease of the fingers and the knuckles. nobody likes a streaky elbow do they? so by moisturizing these places will reduce the risk. ohh that sounds fancy haha
3: use a mitt: this doesn't just stop your hands getting that horrible orange/green colour from applying the fake tan it also helps apply the fake tan more smoothly. i advise use a 3 in 1 mitt i personally use the solkiss 3 in 1 applicator mitt this has a exfoliating side where you can rub of any excess dead skin, the applicator where you apply the fake tan and buffer where you can buff off any excess fake tan, this also comes with a pair of gloves which are handy.
4: use a fake tan which the colour goes straight on this shows you if you have any streaks which you can then correct later on. the fake tans i use which are good for this are, st.moriz lotion or mouse and the sun-kissed mouse
5: finally once the fake tan is applied do not apply your clothes until the fake tan is completely dry, normally fake tans dry quite quickly now so you do not have to wait a long time.