Never use a tester on your lips -- it's unhygienic. Test lipstick on your fingertips instead of the back of your hand: the color and texture are closer to that of your lips.
If you want your lipstick to last, use pencil first as a base. Outline and color in your lips with pencil (nude, if your lipstick shade is light) and slick your lipstick on top.
Your lips will also look softer, "smudgier," and less defined if you don't use pencils or lipliners.
To avoid lipstick on your teeth, after application, run your index finger through the middle of your lips and pull it back out. The excess will come off on your finger, not your teeth.
In a pinch, your lipstick can double as blush. (But never use blush on your lips.)
Outline your lips in pencil before you apply lipstick or gloss if you don't want your lipstick to feather.
Store lipstick and perfume in the refrigerator. It will last longer.
If your lipstick shade turns out to be brighter than you thought it would be, color in your lips with a pencil a few shades darker than your lipstick (for instance, brown pencil under dark red lipstick) and layer the lipstick on top. Or coat the lipstick with a darker lip gloss, which will turn down the heat.