Keep in mind that sex should be a fun adventure between consenting adults. Do you know what turns your lover's crank the most? The quickest? (Does your partner know that about you? Have you let your partner in on the secret?) Use your intimate knowledge of your partner to kick-start the desire, and don't be afraid to ask for what you want. Just be sure to speak in positive terms until you are heard. "I'd love it if you would ..." will get you way more action than any "You never ..." ever could.
You might also want to consider adding a new dimension to shake up your routine. Hang up the "Do Not Disturb" sign and surprise your lucky lover with some role-playing, cosplay, sex games, or porn to perk up your appetites.
Last, but not least, shared enjoyment of non-sexual activities, like hiking, biking, kayaking, camping, picnicking, or whatever it is you enjoy doing together is also important, because it creates the intimacy upon which your sex life is ultimately based. Don't relegate the time you spend together to sitting in front of the tube or playing video games; it's just not sexy. However, a walk in the woods might be very sexy. When was the last time you and your partner spent the day together, basking in your shared connection? Best lube, bar none.
Finally, keep an open mind to the other person's needs and desires. Sexsmith knows couples with passels of kids and piles of bills who still manage to keep that fire aflame decades into their unions, all because they pay attention to each other's hopes and desires, wants and needs, while encouraging open communication.