Here are a few tips:

1. Avoid getting too many layers cut in your hair. A few are good since they'll give you more bounce at the roots but too many, especially at the ends, can make your hair look scraggly.

2. Don't put conditioner on your roots, it will just weigh your hair down.

3. Use a root lifting spray before blowdrying your hair, then flip your head upside down to dry your roots, it will give you more volume.

Hope this helps!