1. Don't be predictable
If you've been together for a while, this can definitely be a problem. Part of the reason why things were so hot between you and your woman when you first got together was because you didn't know what to expect. If you've been together for a while and want to maintain the same similar level of excitement with your woman as you did when you first got together, you have to keep it fresh. Master the art of foreplay and avoid the same old grunting or repeating certain words. Telling her that what she's doing feels amazing, that she looks hot, or what you'd like to do to her or have her do to you can also be a turn-on for many women.
2. Don't ask for permission to have sex.
A good lover can do something as simple as give a woman an intense look or use a certain touch to let her know he's in the mood and turn her on without ever having to ask permission. Most women don't find a man who asks for permission very sexy and see it as a "rookie" move.
3. Don't always have sex in the same location
Use your imagination and make simple changes in the locations where you have sex. The possibilities are endless. Try the shower, the kitchen, the living room, the car, etc...
4. Being afraid to experiment
Talk about what turns you on with your woman. Trying some new positions or engaging in role playing can make for better intimacy and keep you both turned on and spice things up in the bedroom. Try new things that you'll both enjoy and never let your sexual encounters become routine to the point where she can anticipate your every move and never underestimate the importance of foreplay for a woman.
5. Not going the extra mile
If you want to prevent her from ever being bored with you sexually, you must put in some effort every once in a while. You have to be romantic. Leave her love notes describing what she should slip into or out of while she awaits for you to come home. You can also seduce her by trying things like making a romantic dinner for two and playing some music to get her in the mood, and giving her sensual baths. Make it about pleasing her next time and she may just do something to please you in return.