Find a quiet place where you won't be distracted by people, cell phones,computers, TV's etc. To start you may want to try this for about 10 minutes then extend the time as you feel more comfortable.
There is no need to sit in the lotus or half lotus position, you can sit cross legged or on a chair. If you have difficulty sitting due to illness or injury you can lie down. Make sure you are stable and comfortable, you don't want to be moving around too much. Sit with your back straight, your hands on your lap and your eyes closed. You can use pillow(s) to sit on to make yourself more comfortable, zafus
and zabutons are great for this. If you have trouble with your knees or hips try a mediation bench (see image below) . Have blankets or shawls on hand in case you get cold since you will be sitting still. Keep some water to drink nearby as well.
You can find meditation pillows and benches at specialty stores or online, though they can be expensive. Meditation benches can cost around $70-80 whereas I made my own for about $10 worth of material and an hours work (you can find instructions here