Overall a willingness from both of you to hear each other and work together
Do you know what style it is?
I do a specific form of couples therapy (rather than counselling) that impacts how it is structured. Id be starting with some basic aims, and some feeling out of your surrounding structures, how you got to where you are
What i usually advise my couples is that im not there in the role of judge. Sometimes people expect me to tell off one partner, take a side etc. Its not a space for punishing either party.
This can be really tricky for people especially in cases of infidelity.
My aim is to get couples communicating better usually. My aim isnt normally to preserve the couple at all costs. Sometimes when people are able to clearly talk things out, lay out wants and boundaries you might decide that your partner cant meet yours or you cant meet your partners.
I'd caution against it in cases of abuse.
The other thing I would usually say is that you both need to be open to change, taking some responsibility and it will be work. Its absolutely alright if you are just done and no longer want to work at it and are just done.
Sometimes people feel like they "should" do it at a really late stage to validate breaking up. You dont need my permission
Equally its really great when people come early on before there is massive risks. Like a physio or other type of counsellor prevention is better than cure and things dont have to be bad before you get some help
Trite to say but there's no magic words, magic words in the right combo to make people different, its just work!
Ideally people come willing to go to a reflective space, where there is less self defensiveness but genuine openess. Its okay to come frustrated, angry, sad etc but you have to be open to moving past that. (If you've been really wronged, its okay to be furious, and want to stay furious for a while!)