Look there's a whole bunch that goes into a GF / Wife and sex.... She generally needs to be in the mood, not just in the mood, but in the mood to do it with YOU. If you treat her like an ass then she'll clamp her legs down tight. Get romantic with her, I don't mean buying her flowers and stuff, I mean just give her more attention, let her know she's on your mind.
If your wife likes getting massages as my GF does then its the best kind of foreplay out there. If she just likes the occasional massage start her off with some light massage when she's clothed, while you're watching TV, on her legs or shoulders....
Tell her it will feel better with massage oil which of course needs to be done in bed and of course and oil massage needs to be done naked or almost naked, get a light massage oil, baby lotion is ok in the begining. Give her a caouple good massages DON'T GET HAM SUP i

n your first few massages! Keep you hands off her privates, but you can get close!

But you need to kiss her every now and then, everywhere, arms, legs, shoulders, butt cheeks.
Start on her shoulders, back, lower back, move on to her her butt and the sides of her butt, NOT THE BUTT CRACK!!, choose a leg start on her thighs, move to her calves and back to her thighs, do the same on the other leg, finish off on the feet. This should take you at minimum 45 minutes to and hour!
Don't worry if you're rock hard while doing the massage let your cock touch her naturally, this lets her know that you want her, and that she's still desirable to you. After the veggie massage she might be the one to initate sex...if not keep being patient...
After a few veggie massages with baby lotion, switch to a more musky, minty scent, lavender is good with a bit of peppermint, don't get too musky with something like patchuli. The air will get more rich with the musky scent, your massages can get a bit more "HAM SUP", near the end of your massage brush up against her privates as though "ACCIDENTLY" when you're doing her thighs. The peppermint will have a warming / cooling effect on her pussy and clit, it can/may stimulate her sexually.
You'll have to judge her reactions to the accidental touching, she might give you more space to give your hands access to her privates, she might lift her ass off the bed a little as you touch, not moving at all is still good as long as she doesn't verbally complain...i've often found my girl dripping wet by the time I get there, if she's responding have a "few" more accidents heheh....joke about it with her, get more persistent with the touching, if after a few touches she seems to be responding you can just get 100% ham sup and stimulate her in earnest, rub her clit for a while, stick a finger in, your other hand can still be partially giving a massage. If you get this far....just start fucking her or flip her over and fuck her, trust me she will be wanting to get fucked. After you've had one of these sexual massages she'll be looking forward to them in the future.
One thing about massage oils, keep the oil light, a thick massage oil will not go down well with her, she doesn't want to be all sticky and neither do you. Don't use too much. If you mix your own oil don't use too much essential oils relative to the base oil, if you use too much of an essential oil it can become a skin irritant. get good quality essential oild, don't buy the cheap shit.