My husband started off hating Disney. He went once when he was young. His parents took him to a character meal and Goofy wouldn't stop messing with him, so he kicked Goofy (and then got kicked out).
After we met, he went because of me, and now, after 3 trips, he loves it almost as much as I do. Here's what I did over 3 trips (2 at Disneyland 1 at WDW) -
Definitely catch the fireworks from a good viewing location, even if it means missing something else.
Excitement is contagious - I get so giddy and can't stop smiling when I'm there. That feeling helped carry over to him. Go with a no complaints/all smiles attitude.
Take a break - When you're not a huge Disney lover to start with, hitting the parks at full force from morning to night will make a hater, not a lover. It's exhausting. Take a nice long break in the afternoon to kick back in the hotel or pool and relax. I have snacks, beer, and vodka in the room so he can have a drink or two and zone out. I also go with the attitude that I'll hit all my favorite rides, but if I miss some others, it's ok. I stay flexible and if I notice that any of us are getting tired or cranky, it's ok to take a break early. It's better to miss a little and enjoy all you did, than to push it and get cranky for just one more ride.
Minimize crowds - Long lines can be a bit much for some people, especially if they're only kinda into it in the first place. Get to the park early when it's least crowded and use fast passes as much as possible. My hubby loved that we didn't have to wait long for anything, and he never had to say "we waited an hour for that crappy ride?!!" Short wait times made every ride better to him.
The thing that really hooked him, other than my contagious excitement and the fireworks was the food. I poured over menus and chose according to what I thought he'd like best. At DLR, there's a nice mixture of counter service and table service restaurants, and of course all the tasty snacks. At WDW, I did the deluxe dining plan and we did sit down meals for all but one. It's been 6 months since our trip, and he still talks about how excited he is to go again, and how we have to eat at Ohana's every night we're there. lol
My hubby is also a huge sports fan, so if there's an important game, I make sure he gets one of those super comfy lounge chairs at ESPN. It helps that he doesn't feel like he's having to sacrifice something he loves just for the parks.