A few tips:

Climb to your high point and try to push through. If not, feel all holds to think about/put together a sequence. Then down climb to your last comfortable spot.

Remember the down climbing/reversing sequence. I worry more about reversing 15 difficult moves or so without tripping over my own feet, more than I worry about knowing whether or not I can eventually put the moves together to top out.

I've had good luck with 0's, 00's and 000's; placed close together and for shorter falls.

~~TMS~~

You're fucked.
Seriously though...slip.
Down climbing is extremely important but you must prepare for the moment beyond retreat. If you cannot get your noggin on lock down and push through, yikes. Listen to your inner fear and figure out when you can trust it.
Better to be cautious than dead.

Are there ways that your belay can help? I've seen in some of the grit films sometimes twin ropes can help and sometimes your belay can run the opposite direction to keep you from a ground fall. Also a few pads may help. When I personally have done R climbs I tell myself over and over "no room for those thoughts, keep moving". But look at the bright side, soloing is way easier since you don't have to bother with gear.

You should have confidence in your ability to deal with the unknown, and confidence in your ability to climb at certain grades. If you aren't used to climbing high above gear on routes that are easy to moderate for you, then you're probably not ready to do so on hard routes. On the other hand, if you're happy soloing and climbing high above gear, maybe it is time to see how hard you want to climb w/ little to no protection.

Mentally bolt it.

Sometimes it's necessary to just 'throw the switch' and go for it on a route. But I've downclimbed and backed off plenty of stuff if it didn't feel right. I have obsessed about a route enough that I got up in the morning and was properly psyched for Route XXX that particular day. I'd recommend soloing a few easy routes to get your brain in shape, be prepared with a downclimbing option (I wrote a tech tip for Climbing a few years ago that's on their site), and be sure to have a belayer you can trust. A great belayer can really inspire me when I know that they're gonna catch me no matter how sketchy the situation. Bonus if you've got a belayer who's already done the route.

+1 for the ability to downclimb, which has saved my ass (with and without a rope) more than once

Nobody has yet mentioned The Rock Warriors Way by Arno Ilgner. That book is all about psychologic strength. I read it and then soloed Petit no problem. Gettin laid all the time now too

nothin but practice, gotta start with windmills before you slay giants.

If you have to ask, you probably shouldn't do it. But, if you think you are ready, this is the best advice here from someone that has really done it. All the rest are toproping, rehearsing wanna be's. Sorry wankers. No offense.

All things considered, you'll figure it out when you get to the bottom of the climb. It will either feel right or it won't. Don't force it and don't push it too far. However, as Mic said, sometimes you have to 'throw the switch' and go for it. You'll know it when it happens.

I hate giving this advice because it's a personal decision and yours alone. It's also a dangerous question that will invoke a wide range of comments.

Good luck

Belayer story: The first time I led Jules Verne, I had Candelaria holding the rope (like money in the bank). I climbed up the runout, got shaky, then climbed back to the rest. He yelled up "you were already past the crux!" As I recall, when Caylor wanted to lead JV, he called me to belay. I was glad to pay it forward.

I have nothing to add to this wankfest, yet I feel like I need to be a part of it.