If you can't make it to a crystal store, so you're ordering online, then there are three crystals I believe everyone needs that should be among your first purchases.
Rose quartz is a crystal of unconditional love, romantic love, and forgiveness. It supports the heart chakra, and it has a peaceful and calming energy that can help you vibrate at the frequency of love. It can also support compassion and kindness. I recommend working with rose quartz if you are looking to forgive yourself or another, if you'd like stronger relationships, and to strengthen your compassion. Wear it as a long necklace (at about heart level) or place it near where you meditate.
Clear quartz raises your personal vibration, supports spiritual growth and connection to the divine, and amplifies other energies. It's a great crystal to use when you're feeling joyful (or some other positive energy) and want to bring more joy into your life, because it amplifies that energy. If you're feeling cranky, then you may wish to avoid the clear quartz until you are in a better space emotionally because it can amplify the negative emotions just as easily as the positive.
Clear quartz is also a good stone to use in conjunction with other crystals because it amplifies their energy, as well. So if used in conjunction with rose quartz, for instance, it can amplify the vibration of unconditional love. I keep clear quartz in my meditation space to strengthen my connection to my higher self and to the Divine, which I seek during meditation. I also hold it during affirmation or visualization because it amplifies those energies, which can draw them to me more quickly.
Citrine is a form of quartz (as is it's close partner, amethyst). It supports the third chakra, which is your center of self-worth, self-esteem, and creativity. Citrine is also a stone of manifestation, and it can help you manifest abundance - it is a prosperity stone. I wear a pear-shaped citrine ring on the desire finger (index finger) of my receiving hand (in my case my left, because it is my non-dominant hand). The narrow end of the pear shape points towards my hand and arm to direct the energies of prosperity, creativity, and self-worth from the universe to me. So I'm using the shape of the ring and pointing the wide part like a funnel at the universe to funnel prosperity, self-love, and creativity to my receiving hand. For prosperity, you can also place citrine in the prosperity corner of your home (the back, left corner of the house when you stand at your front door facing into the house), or put it in your wallet or cashbox. For creativity, keep the citrine near where you create, such as on a workspace or in your kitchen, for example. For self-love, wearing citrine as a bracelet keeps it at about third chakra level and can help strengthen those feelings. You can also hold it when you affirm or visualize.
Want to learn more?
I have a crystal healing class coming up at Vision8 Studio in Portland on November 12. Seats fill up quickly, so pre-registration is required. The class is $25.
My newest book, Crystals for Beginners, just released on Tuesday.