1) clean all the old wax off your board...properly. Use a plastic scraper, then hot water & detergent, scrub the deck with a good stiff brush and then dry it.
2) Go to a surf shop and buy the correct wax for your temerature range. Why not buy half a dozen cakes while you're there, that way you don't have to waste your life on stupid shopping trips to buy new wax every month or so...
I use Sex Wax, it's the best brand in my opinion...it beads up well, doesn't fail and of all the waxes I have to comb it the least.
3) mark out roughly the area of the deck you need to wax, you don't have to do the whole deck...unless you stand & lie all over it. I just do a smallish square (about 2 foot square) near the middle where I lie with my chest & stand with my left foot.
4) Wax it properly, until you get nice little humps, do this initial coat when the board is cool and the wax is also...it'll bead up better and get a good solid grip on the surface. If you live in a hot climate stick the wax in a fridge or something for 1/2 hour beforehand.
After that you'll be fine, this good coat it should last you for several months if you surf daily or twice daily, but you will need to give it light re-wax after each surf...when I get home I give my board a fresh-up and at the same time check for minor dings, check leggie cord etc.
I never need to take wax or a comb with me, my boards are ready to go the instant I hit the beach. It's a good routine to get into.