From experience - you need to go prepared with details of all your income and outgoings, who has contributed what to the household expenses including the mortgage. Details of your anticipated pension as this can be taken into account when divvying up your assets. Details of debts (singly and jointly).
If it's any help to you, our solicitors agreed a separation order between us at the time we split, because that document made it very clear from the date of the split who was living where, who was paying for what - my ex stayed in the house but bought me out (he wanted to stay there, I didn't). We were then able to use that document and when we wanted to divorce amicably two years later, there was no further discussion about finance, it just went through.
I hope this helps.