Well, I certainly do not know what your sex life has included over the years. I do know that after being with my husband for 13 years, things got boring for both of us. So much so to the point that I often fantasized about threesomes, although I would never actually do that.
We just began to experiment with some other things. More anal stimulation, both him and myself. Sex in different places. Once even outside on a cliff behind our house that overlooked the town. Fingering or blow jobs while driving. Toys. He even asked me to masterbate in front of him, and to either tape myself doing it, or tape our session while in bed. That only happened once because he didn't like how he looked on camera...Lol.
Spontaneous moments help. Variety helps (the place, position, toys, etc). Setting the mood helps. You can try feeding each other different erotic foods, and then using them in/on your body. Flavored massage oils. If you are comfortable enough with it you can even get into role playing, bondage, etc. There are also love making, or couples, coupons that you can print on-line that describe different acts to do.
Be creative. The only thing that you should do before hand is maybe talk to your partner about how far you both are willing to go with it. You, or him, may have some bounaries to define what you would, and would not, be willing to try/do.
