Many people rely on the same old ways that may lead to satisfaction, and after a while what used to work becomes stale, so to speak. When I work with couples who are in a sex rut and want to spice it up, I encourage them to make a list of all the things they need, want and desire, as well as what they want to try in and out of bed. What's on your bucket list? Compare things that are similar, and be open to trying what your partner suggests (assuming it's safe, consensual and potentially pleasurable).
Out of Bed: Remember what it felt like when you first met? Increasing dopamine levels, by doing novel things can surely make things spicy again. It doesn't mean you have to go skydiving, it can be as simple as cooking together, going to a show, exploring a new place in your city together - along similar lines to what Dr. Season said. Do activities that engage the senses. Remember, foreplay begins before you hit the sheets. So, even if you do an activity that's not sexual, it can definitely increase your connection to your partner and make you feel closer - the perfect set-up for hot sex.
In Bed (or wherever you may want to get it on): What have you been wanting to try, even if it's just once? It may be certain positions, sharing fantasies, experimenting with toys and other props like bondage tape, erotic talk, etc. If you need ideas, go to the bookstore and flip through books that lists a ton of things to try. Pick out your favorite read and buy the book. Later when you're home, close your eyes, flip through the pages and point to something you'll try that night. Some of my favorite books are listed here: http://www.igniteyourpleasure.com/store/
Look at each other without looking away.
Every day, tell your partner one thing you ordinarily wouldn't tell them.
Be prepared for them to do the same.
Feel each other's heartbeat.
When out to dinner, don't sit at a table.
Sit at the bar.
For example, if you live with your partner, you could commit to greeting your loved one at the door with enthusiasm and excitement each day. A friend once told me "greet your partner at the door the way a dog greets you when you get home." It sounds like a funny concept, but it makes sense. Think about how good it feels to come home to your puppy because of the dancing, joyous reception they give you! It makes you feel special and appreciated. Even if you are busy, tired, frustrated, or right in the middle of another project, you can commit to taking 5 minutes to put everything else aside so that you can shower your partner with affection and love when they walk through the door. At the end of the day we all want to feel special and this is a simple way to do that in a relationship.
The other part is small acts of affection expressing your gratitude. My favorite is writing something in lipstick on the bathroom mirror. How about a sexy text message or note? I always say that foreplay starts from the moment you wake up and when you appreciate your significant other on this deeper level, the physical can only HOT!