hey great start! i agree with most ppl here and their great advice stemming from experience.
here's a few things i like to keep in mind;
1. if you're doing a mixed reef (corals and fish) then make it both coral and fish friendly by...
2. allowing plenty of swimming room while providing hiding areas such as caves and crevices.....fish like to "hide" themselves from others even if it's just going behind a pillar.
3. provide ample areas for coral placement and their growth. it's one thing to place frags or colonies on ledges or outcroppings but with the proper lighting and water quality your corals will grow!
4. allow water flow to be able to circulate around the perimeter of the glass as well as through caves and under ledges. this decreases the amount of detritus buildup and further issues with nitrates.
5. don't forget that this is a reef for your fishes, the corals, and also YOU! so it's an extension of your personality as well as a means to be creative. HAVE FUN! HAVE FUN, and HAVE FUN! there's plenty of people in this hobby that get very very technical and serious which is ok. but i say to always have fun while providing a great habitat for your corals and fish and this hobby will pay more dividends than any wall street stock ever could!
good luck and keep posting pics!