I'm not an expert, but this is what really helped me and I am told I am now taking professional quality pictures.
Think about the the subject matter and conditions you will be taking pictures in. Let's say Costa Rican landscape. Start taking pictures right now with conditions as close as you can get to what you will be shooting in Costa Rica. Keep a record of your settings or just look at at the settings you had your camera on in the photographs. Trial and error and the prosess of elimination will soon have it to where you can look at your subject and set your settings at the drop of a dime or have them preset. If you don't do this trial in error now you will be doing it in Costa Rica.
A professional told me "Get to know your camera like it is an extension of you hand and eye, the only way to really do this is to take ALOT of pictures."
She also told me new photographers have the great blessing of being able to take as many pictures as possible with no cost or dark room so take advatage of it because it is invaluble.
Also you or your subject might be moving so you can't always pick you aperature. If you try to stay with one aperature you will miss many good shots.