How to select your crystal
First things first: Identify what you feel you're missing before looking into what stones can provide you. This will help you indicate what's going on within yourself before depending on outside sources.
From there, just let your intuition choose what's best for you. Whether a crystal catches your eye or you can feel a physical pull toward one, your inner subconscious will help guide you to the crystal that's right for you. Once it's pick out, you can create the connection you need.
How to care for your crystal
When you first bring your crystal home, you'll want to cleanse away any negativity it may have picked up. You can hold it under cold, running water from a tap or rinse it in a natural source of water. Either way, be sure the water is cool, not warm or hot.
Add a bit of sea salt to the cleanse or burn sage to really help it get rid of unwanted energies. You can also leave it out to dry in morning sunlight or full moon light to let the light filter through.
It's not just about their physical care, though. For crystals to work their magic, you mentally have to remove the negative energy or skepticism you may have about their capabilities. It's important to respect what they can do for you.