Never use a tester on your lips - its unhygienic. Test lipstick on your fingertips instead of the back of your hand: the colour and texture are closer to those of your lips.
If you want lipstick to last, use pencil first as a base. Outline and colour in your lips with pencil (nude, if your lipstick shade is light), and apply your lipstick on top.
To avoid lipstick on your teeth, 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.
Outline your lips in pencil before you apply lipstick or gloss if you don’t want your lipstick to feather.
If your lipstick shade turns out to be brighter than you thought it would be, colour in your lips with a pencil a few shades darker than your lipstick and layer the lipstick on top. Or coat the lipstick with a darker lip gloss, which will turn down the heat!