Be prepared that your SO is not perfect. Each of you will have life long habits that you consider "normal" or "the right way". For anything from putting down the toilet lid to the way you pack the dishwasher. Even though there are going to be some things that drive each other up the wall, soldier on through and except each others differences. Be grateful that your SO packed the dishwasher at all.
Learn to compromise. Again, there are going to be differences and some of the time neither of you will want to budge on a certain topic. So you will need to talk and come to a compromise and work out a solution that works for both of you for issues that you both want your own way on.
Will you move into their place, they move into yours or will you find a whole new place together? Sometimes it's a good idea (if possible) to go flat hunting together and choose a new home together. This should help dispel any feeling that your SO has moved in on your turf which may in turn lead to resentment. Moving into a new place together lets you both decided how the pantry is stocked and where the couch and TV should go and what pictures are on the walls.
You both most likely work full time, so equally sharing responsibilities is of the utmost importance. When one person is doing significantly more that the other, this will most likely lead to animosity. For example, if one of you is a terrible cook, don't rely on the other to cook all the meals but instead get involved and cook together and learn from your SO. It's also a great way to chat and wind down together and bond after a long day.
Split all bills evenly and make sure they are paid on time. Think about setting up a joint account for you to both put your share of the rent, internet and utilities, and put a percentage of you weekly income in so you are not stuck with large bills you may not have saved for. If you don't want to set up a joint account then make sure you have your own separate savings account to put your bill funds into. Never reply on your partner to pay the bills for you because you have forgotten to set aside funds in preparation.