I have. It's probably my mother coming out in me, but it's something I definitely notice and it usually ends up bothering me a little (OCD, much?) ha! There are a couple of fail-proof tips that can help you hang that piece of beauty in the most perfect spot.
1. The top of the frame should never be higher than the door frame. There are always exceptions to this rule, especially with big art pieces, but as a rule of thumb, if you have a 'regular' size piece of art or smaller, make sure it's not sticking up higher than your door frame.
2. The rule my momma always taught me was to hang your picture at eye level. This can be tricky since we're not all the same height. So, we will go off of the average eye-level height of a person at 57". The center of your wall art should be at 57". This is probably not where your nail/hook/wire/whatever is. So...
1. Measure and lightly mark 57" on the wall
2. Measure top of your picture to the middle (or take height and divide by 2)
3. Measure top of your picture to the tightened wire (a small amount)
4. Subtract this last amount to tell you how far above 57" your hook should go
5. Measure up from 57" with this last amount and lightly mark on the wall
This also works for hanging groups of pictures. Just always remember the CENTER of your picture (or group of pictures) should always fall at 57 inches from the floor.
Some picture hanging tips that I've seen on Pinterest:
Hope this helps!