A bit of time on your own together, with no kids. (well everyone needs a fantasy!!!).
Better sleep. Dressing up smartly and going out together and generally being a couple - reminds you why you fancied him in the first place.
You can also have some hormonal treatment but thats a bit extreme I know. The reason I know this is I am in my 40s and have discussed the decline in libido with doc as I thought I was menopausal. I got referred and the consultant said a bit of testosterone could help sometimes. But blood tests revealed that my oestrogen was low and so I got low dose hrt. Just started it and feel a bit better, but circumstances mean we currently get no time!
I was also told at the clinic about a (embarrassed cough) device called eros that they use in the US ... I will let you google that! They are very costly but apparently there is a UK equivalent that is cheaper. Research shows it works by increasing blood flow to your bits, but I cant vouch for it because I didnt bother.