Communication with her caregiver(s)
Talk with each other before the labour. Familiarise yourself with what is important to both of you, for the labour and birth. Communicate with her throughout the labour. Your plans may change, as the labour unfolds. Listen to her and support her choices. Liaison with her caregiver when necessary.
If you have particular needs that are important to you both, then it is necessary to make these needs known to your caregiver and staff. This can be done prior to the birth (if you have your own midwife or doctor), or on an ongoing basis verbally with the hospital, or birth centre staff, or in the form of a birth plan. You may wish to read birth plans.
Stay calm
If you are experiencing feelings of being anxious or nervous, she will pick up on them. You can only feel what you feel, so look at taking a short breather, perhaps debriefing with your caregiver, or trying some deep breathing to ground yourself.
Try to avoid conflict with her other support people, if possible. Potential personality differences should be considered when choosing the birth team. If you are creating bad vibes, she will be too concerned about all of you to get on with the job at hand. If conflict arises, defuse it, deal with it (or one of you leave). It is not worth disturbing her rhythm.
If things start getting out of your control with regards to emergency medical intervention, stay close to her, speak with her, and talk her through it. You may be nervous, but she will probably be feeling worse. She needs you to be stable through this. Try to hold it together until the crisis has subsided. Ask your caregivers to explain what is happening as things unfold. You may need to debrief with staff after things have calmed down.
Don't complain or place demands upon her