Do it just for you, to practice on others you need to be attuned by a certified Reiki Master and join a union. In your day to day life learn to take a moment just for you. You can use breathing techniques, visualisation and hand placements to keep your well being topped up.
Creating a habit is the best way to incorporate positive change. Try every morning or night to think of three things you are grateful for (although this is not necessarily Reiki, I think it's just a good habit as gratitude is a wonderful gift - "Find three good things each day. People who are grateful tend to be happier, healthier and more fulfilled. Being grateful can help people cope with stress and can even have a beneficial effect on heart rate. ... Science is showing that gratitude is important for how good we feel psychologically and socially." - Three Good Things - Action for Happiness )
Briskly rub your hands together and place on the crown working your way down your Chakra's, spending a minute or two to breathe and be grateful. If you like you can visualise the colour of each Chakra, see image below. Breathing technique: Inhale through nose, exhale through mouth with a sigh... try a couple of rounds slowly.
If you have any for of anxiety of tendency to have panic attacks avoid practicing breathing techniques alone maybe try a yoga class or meditation class. The most important thing is to listen to your own body only do what feels comfortable and right for you.
Visualising yourself in a white light before you start your day is a simple beautiful way to use reiki.