I am often asked how couples can prepare for their first counseling session. Since you are seeking counseling at all, it tells me that you value your relationship. To that I say, congratulations for having the courage to seek help.
Usually, couples arrive at the first session thinking that their problems are caused by the other. They are in a cycle of arguments that sound like, "If you would just do (or stop)....then we would be fine". Or, couples feel disconnected and lonely and want to be close again.
To enhance your counseling experience it might be helpful for you to think about what you want from your relationship. You and your partner are two different people and your relationship is a third entity. What is good for one of you, may not be good for the relationship and vice versa. It is sometimes beneficial to think of this as a three legged stool. One leg represents each of you and one leg for the relationship. The stool needs all three legs to stand. As you enter counseling, think about what you can do to enhance the relationship leg.
Counseling is all about change, but change being as unknown as it is, can be unsettling and downright scary sometimes. It is practical to think about what you can change about yourself, rather than what your partner can change. Primarily because you have direct control of yourself and not your partner. If you are both able to do this, the couples counseling will have a greater chance of success. When partners try to change the other, it doesn't work out well. That said, be honest and realistic about what you want from your partner. You can have wishes, desires, and boundaries.
It is valuable to think of your relationship as a system. One part will automatically influence another in a circular nature. Think of it like a thermostat in your home. If you leave a door open in the winter, the heat needs to kick on harder to keep the temperature the same. In much the same way, couples cause each other to "heat up" or "cool down" based on repetitive behavior patters. The counseling process will help you uncover these patterns and enlighten you in ways to enhance the relationship.
A final thought, remember the difficulties in your relationship took time to develop so it may take some time to undermine them to repair the relationship. Like anything you want to change it takes awareness, focus, time and effort. The end result is well worth it.