The first thing you need to do is choose a shape that's right for you. Handlebar, cookie-duster, lady-tickler... The possibilities are endless, and it's a great way to showcase your personality. Once you're set on a style, quit shaving before the weekend or going on vacation: It will save you some of the embarassement of having to go through the unsightly growing phase in front of your co-workers.
Once you've got a nice full 'stache, keeping the look up is easy. Shave your entire face just outside the line of your moustache and save the finishing touches for later. Unless you want the pencil-thin look, do not shave the hair under your nose or your whiskers will look C-shaped.
All you need to keep your moustache neat is a small fine-tooth comb like Kent Moustache & Beard Comb ($6, at Barber & Supply) and safety scissors, which will give your more precision than a trimmer.
Cut the hair around the edge of your lips in the desired shave, and follow the line of your upper lip to clean up the bottom of your moustache. Make sure your moustache looks symmetrical. Keep trimming the hair as soon as it reaches your lip: After a week of upkeep, you'll have a beautiful bristle.
Your moustache should be an invitation to kisses: To keep the hair smooth, moisturize your moustache with your usual lotion as if you still had a naked upper lip. You may add a drop of Kiehl's Creme with Silk Groom ($18, 4.2 oz) for extra lusciousness.
For more elaborate styles like the handlebar, get some wax. Firehouse make two shades of wax for light or dark hair, which will enhance the natural shine of your whiskers ($13 per 1 oz tin, at MiN New York). Or if you want to go for a classic, get Gold-Dach's Bartwichse Hungarian Moustache Wax ($28, 0.5oz), used by Salvador Dali on his legendary moustache.