Sit in a posture that's comfortable and stable (see below).
Refrain from eating at least 3 hours before meditating.
Wear something loose. Or nothing.
Breath slowly from your belly. When you inhale your belly expands and when you exhale it contracts.
Sit every day.
(I like meditating in the morning, first thing after getting up. I sip a little water and then meditate.)
Meditate for 10 minutes at first then work up to 30 minutes.
Then try meditating twice a day. Or 3 times or more.
Try meditating longer too.
Experiment with your meditation schedule. Do what works best for you.
Sometimes, when you have a few free days, try dedicating all your time to meditation.
Meditate. Go for a walk. Mediate. Clean the house. Meditate. Etc.
Sitting on a seiza bench
Half lotus on a pillow
BKS Iyengar doing Lotus and Siddhasana