I'm going through This at the moment
Go on the government website for divorces as that has information on time lines etc
Start a file on the computer/hard copy of relevant information like pension statements, finance agreements etc
Go in with a plan of what you'd like - when i saw my solicitor I basically had an idea of what split I'd like and wanted to know if it was reasonable or not
Start looking at supporting evidence and keep copies in the file - for me that was things like job adverts to show STBEXH isn't maximising his income. Rightmove information on what rentals are available. The free calculators you get on bank mortgage websites so show what you'd be loaned on a single income and also him.
Look at all your finances - when debts are due to be paid off, when fixed rates are ending etc
Basically build up a picture of what life would be like financially for you and him post divorce
Don't agonise over keeping the family home - it may just not be right for you to do so and courts prefer a clean break.
Speak to the mortgage company about whether you can afford to buy him out
Solicitors are expensive so it's about making the most of the appointment - go in with set questions you want advice on/answers to