When I first started using crystals I chose to go with ones that matched the color of the chakras. Here are some suggestions:
First, I always use hematite near the feet to ground excess energy.
Root: black/red: obsidian, garnet, red jasper
Sacral: orange: carnelian, sunstone
Solar Plexus: yellow: citrine, topaz
Heart: pink/green: rose quartz, aventurine
Throat: blue: sodalite, lapis lazuli
Third Eye: purple (others use indigo): amethyst
Crown: white (others use purple): selenite, opal
I also use quartz points in the client's hands, point pointing towards the palm of the receiving hand (non-dominant) and pointing towards the fingertips of the giving (dominant) hand.
That's a good place to start.
Now that I have been working with crystals for a while, I usually just pick crystals intuitively for each session.
Hope that helps!
Sally