One thing you need to be really careful of at this time of year, is condensation! Also do not spray if it's cold, as it can cause blooming ( a milky discolouration)
You can buy PANEL WIPE for cleaning all the surfaces first, all the car paint factors sell it. Using spray cans is quite an expensive way to go, as they only put a very thin coat on. The more you use, the easier it gets, speed and distance from the panel is very important. Make sure you have plenty of light too, what looks ok in the garage light, may look awful in broad daylight.
Good luck!
John
JFDI
(Just F*****g Do It)