Keep as upright as possible. Pressure is a natural anaesthetic so the weight of the babys head on the pereneum numbs it nicely. Use a position that it comfortable to you. Birthing balls or stools are quite good.
Got at your bodies own pace. If you try to rush it you are more likely to get a tear or graze.
Keep calm and relaxed. You don't want to get your blood pressure up or exhaust yourself hyperventilating or pushing for england. Tru to 'breath down' the baby. He doesn't really have far to travel so imagine each deep slow out breath is nudging him down gently and smoothly.
Before the birth practice relaxation techniques - visualisation, hypnosis, whatever relaxes you and try to play the same music as you relax. At the birth, if you play the same music your body will automatically relax as you hear it.
Birth can also be a bit boring so make sure that you have entertainment - music, radio, books, amusing husband, etc. Birth partner also has to keep you relaxed, fed, watered, massaged, supplied with cool damp flannels for your forehead... in fact anything you need to keep relaxed.