So I've been trying to work on my abs without going to the gym (because no time). I've been getting sick of planks and I hate crunches with a passion, so I followed some 
advice and got an ab wheel.
The moment I saw some videos on how to use it, I'm like, "I'm gonna faceplant so hard when I try this". So when it arrived, I tested it and sure enough, faceplant. Obviously, my abs aren't strong enough to keep me up, so more strength and practice in that area would definitely help. But is there anything I can do in the meantime to get there? Some kind of half-rep or something to help me build up my core? Or should I just go back to planks and reverse crunches?
I'm sure you probably are, but you're doing it from your knees, right? Don't try from your feet for your first go.
Aside from strengthening your abs (planks and reverse crunches are good, if you have a pull-up bar, I'd recommend some hanging leg raises too), you should get your triceps and other pushing muscles ready to hold you up. Push-ups are great here. If you have access to TRX straps, fallouts would also be great to do. Nice thing about TRX is that you can change up the difficulty by changing how far away your feet are from where your strap originates.
Part of it is just getting the balance and everything too, which is just practice and occasionally perhaps biffing it. That's where some quasi half reps would come into play. Keep your butt on your heels, start with the wheel at your knees under your shoulders, body already mostly parallel with the floor, then just rollout with your arms, keeping most of your body on your legs and get used to keeping balance with minimal weight on your shoudlers/arms.
It's definitely worth doing ab roller, but you are right that it doesn't really have an easy mode.
Thanks for the advice! It's all very helpful!
I am indeed doing in on my knees, aside from once or twice on my feet to see what it's like. Good call on the hanging leg raises, too. I've been using my pull-up bar quite a bit for my arms, so I'll just add the core to it as well. It's only been a day since I got the wheel so you're right that getting the balance is a huge part of it haha. I'll definitely keep your form advice in mind when I practice.
Sounds like you have the tools to succeed. You've got this.