You are not going to be able to avoid algae. Of course you can do things to slow its growth, but remember algae is a living organism that you will find in any aquatic environment, whether that be in captivity, or in the wild. A couple of people have already mentioned ways to slow its growth. Algae thrives in bright conditions so keeping the lights on all day will encourage its growth. Overfeeding will also encourage algae to grow. High nitrate is also something that helps algae to thrive in a fish tank.
Having said all of this, algae is something that you will have to live with to a certain extent. It does look unsightly on the glass so get yourself one of those magnetic algae scrapers that you put on the inside and outside of the tank. That will keep your glass clean. As for the decor, if you don't like it, you will have the clean that manually because whatever you do, algae will grow.