Strongly Lined Lips:
You certainly want to avoid the 'I lines my lips today' look. Using a black lip liner will certainly put you on the makeup crime list! You should blend your lip liner into your lip to soften any harsh lines. 

Next, apply your lipstick/lip gloss and ensure that it blends well with the chosen lip liner. 

Darker lip shades may tend to make one look older so be wary of this. If you must wear a dark shade, chose wisely. 

LipStick / Lip Gloss Blunders:
A red pout is very sexy, as long as the lipstick stays on the lips and not the teeth. Ladies, be sure to carry a pretty mirror and check your pout from time to time. 

Ever been caught with that 'white line' on your lips? You know the one I mean. This is as a result of your lip gloss rubbing together as your lips touch. Be sure to take of any excess gloss - around the mouth, in between the lips and possibly even on the lips too.