Hi Ronald,
The addition of organic matter such as compost is a great thing to do to improve your soil. If you are going to add sand, make sure it's builder's sand and not play sand which is finer. Don't put more then a 1" layer of sand down. Add to that a 3" to 4" layer of compost and mix it all in to a new planting bed. For a bed that you've already added compost to you can put down a 1" or 2" layer of compost and mix that in.
If you need alot of compost you can use order it in bulk instead of purchasing it in bags as it's less expensive. To determine how much compost you will need you can use this compost calculator.
http://www.cedar-grove.com/compost_calculator.asp
Newt
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.