As the partner or support person, you may feel very in tune with the woman planning a VBAC (or even a repeat Caesarean). Being united and working and planning together will contribute to positive preparation for the birth. Being flexible and open is the key.
For some partners, their own feelings or goals are at odds with the woman. It may be that you want to support her in planning a VBAC but you can't identify with the importance of a vaginal birth. A few men will feel that their partner has become a little 'obsessed'. Alternatively you may feel it is important for your partner to give birth vaginally (or for your baby to be born that way), but you feel she is not that committed to a VBAC.
These are all issues you need to discuss and work through before the birth. If you are both committed to a VBAC then it is more likely to be an achievable goal. Go over any issues that are concerning you, it is better to do this beforehand rather than during the labour, or in the time of early parenting. The woman needs to feel supported, but she also needs to have a positive commitment to planning a VBAC, as ultimately it is her body that will be giving birth. Having you in tune with her will help achieve her goals.