There are various things you can do to maintain spice in your sex
life, but they all boil down to a pair of underlying reasons, and
those're the reasons you need to target with everything you do sexually
if you want to keep things fresh.
Newness is the "novelty" you mentioned, which is experiencing new
things sexually. That's best achieved by actually doing things
sexually... some of the more common ones are:
Some of the "kinkier" things (purely subjective, of course) that
more adventurous couples will try are things like:
All those introduce novel elements that keep things new and exciting
and fresh... until you get used to them. Then you need to add something
The other one is scarcity, which you can ratchet up by:
Anything that drums up scarcity in certain types of sex or with the
partner herself overall works to make sex more exciting, and make you
want it with each other more.