Hi April. To get a fuller sound you need to follow the basics.

1. You need a good mic positioned correctly and good recording/interface equipment.

2. You need to record using the correct input output levels.

3. You need to know how to edit mix and master.

There are tutorials, tips, ideas and links covering all these issues and more if you read all the various threads on Audacity.
Generally the best advice I can offer is I would record dry and then use a little compression and FX depending on the voice and style of song. Use everything sparingly in small increments till you get the sounds you want and save regularily... just in case.