Lots of good advice here.
I would suggest starting out with some quality solo time. Doing things yourself will help a bunch. You have to learn how to relax first and foremost, having a partner there will not make it any easier.
I find a nice warm bath helps to relax not only me but the anus as well. If you have a toy that is compatible with silicone lube you could even play in the tub. Another big help is a vibe, this could be used around the outside if you do not have one that can be sterilized.
Go slow, use plenty of lube and above all else, if it hurts, stop, add more lube, use a smaller toy or your fingers. It will take time but it will be much better for both of you in the end. (oh yes I did