Lots and lots of lube. Then, when you think you have enough, apply more! Start with a finger, then 2. Then, if things still feel good, a slightly larger anal safe toy and maybe more lube. Eventually, a toy nearly the size of your husband, then him.
It can take a LONG time (days, weeks, or months before being able to take his penis) for some.
For us, it was all about me being in control and me being able to completely relax. Just go REALLY, REALLY slow. If it hurts, STOP! It should not hurt.