In the Theravada Forest Tradition the “Meditation on Breathing” is a very popular practice. You can also do body sensation or scanning practice. Loving kindness — metta practice — is highly recommended as well; you could even make that your main technique if you chose. Walking meditation is optional but recommended as a complement to the sitting practice.
Try to have a daily meditation practice of at least 20 minutes per day. Over time you could get it up to an hour a day.
You could start a session sitting with breath meditation for 20 minutes, then loving kindness for 10 or 15 minutes. It’s important to keep up the effort!