There is nothing you can say or do that will "consistantly" return your sex life to the same level it was when you first got together.
If you are lucky though you'll have "magical moments" from time to time. The very definition of the word NEW means FRESH.
What makes sex so exciting with a new partner is NOT KNOWING.
You don't know if they are a screamer or moaner, if they are aggressive or passive. In fact I tell people the most wild sex you will ever have with anyone is during the first few weeks to months you are together. Everyone adopts a "go with the flow" approach with "new partners" especailly if they are (Very Attracted) to her/him and want to IMPRESS. The word NO is seldom if ever used during those first few times something different is introduced sexaully.
Familiarity may not breed contempt but it sure is easier to say NO to someone you have been in a relationship/marriage with for years. A woman that hates violence will go to a hockey game with a "new guy" she has the hots for! A guy with no interest in ballet will accept an invitation to attend a show with a "new girl" he is hot for. Marry these people and years from now they will suggest to each other to go to these outings with a (friend).
Since neither one is no longer trying to impress they are open to being "honest" about how an idea strikes them.
In order to have a chance at sparks in a long term relationship your question can't be, How Can "I"...etc It has to be How Can "We"....etc Unless you BOTH (want the same thing) you will never restore that level of passion. If only one person is striving to ignite passion and romance in a marriage eventually they will resent the other person for not putting in the same effort.
The first step is make sure you're BOTH feeling the same way and (want the same things). From their the TWO of you can plan special date nights, Erotic adventures, or Romantic vacations.
Bottom line if one person is happy with the status quo nothing is going to change long term.