Things Not To Do
White space is not your enemy. It is your friend. Get on a personal basis with it. Learn what it likes and what it looks good in. Negative space is crucial to making a design have impact by enforcing the hierarchy of information.
KISS - Keep it Simple Stupid. Again, don't try to overcomplicate or over embellish your design. Keeping it simple will make it have a greater impact which is good for both designer and viewer.
Don't interpret balance as meaning if there is an element in one corner that it needs to be in all of them, or that it needs to be perfectly symmetrical. You can balance text with a photo or shape. Balance just implies that the design has a balance of visual weight, so it doesn't seem one-sided.
Trapped white space is created when it doesn't have anywhere to escape to. You should be able to put your finger on a chunk of white space and have two ways you can drag it off the page. Trapped white space is a visual eyesore and makes a design look unfinished.
Poor Photo Management
Make sure you correctly resize your photos. When you moven them, make sure to not stretch them - that turns people off instantly.
If you are putting picture on the web make sure you optimize them for the web so you aren't wasting people's time loading unused pixels
No: Comic Sans, Zapafino, Bleeding Cowboys, Papyrus, Curlz or any other cheesy, tacky, unsophisticated, cheap-looking font. Also, limit your typefaces to at most 3.
Don't center everything. It is boring and has little flow or movement.
Remember - Design is as much about skill as it is about taste level. You can learn the programs and the tools, but you can't learn what looks good. That is just something you understand and pick up.