I have a 150 gallon tank and have never been happy with the look of it what can I do to make it look professional?
I usually try to scape with the golden ratio in mind:
http://www.leonardosreef.com/2012/09/using-the-golden-ratio-in-aquarium-design/
Usually I find one or 2 large pieces of deco: (drift wood, lava rock, large stones, etc) and go from there. If you accent the large stuff with other deco that seems to fit the theme, it's hard to go wrong.