It's always easier to ride a horse when both you and the animal trust each other. You can ride a horse that is uneasy around you, but it's much easier when you are both comfortable and steady around the other. However, especially if your horse has been abused in its past, it can be difficult to get your horse to trust you. With time and patience, however, a beautiful relationship can be built.
If your horse has never been mistreated but is skittish by virtue, it will also make it harder for the horse to have faith in you. All it takes is some time together. You need to think through how you wish to move towards him. Make sure you move slowly and approach the horse from the left. If you are walking towards him with anything in your hands, stretch it out in front of you to show him there is nothing to be afraid of whatsoever.
Do not wear baggy outfits when you are moving close to a skittish horse. Your clothing could catch the wind and this can cause a disturbance that will cause the horse to be jumpy. Once they learn to link you with a kind of fear, it will take a far longer time for the horse to gain confidence in you. The horse should never shy away from its owner over anything.
No one should push a horse to do something before he is totally confident. Do get your horse to have full confidence in you before even attempting to get him to do jumps or venture to strange terrain. You can instead have him build up his confidence by letting him jump over smaller hurdles and travel down simple, wide and open paths. If he trips and regains his footing, it might make it that much harder for him to have faith in you while attempting it again and you will also doubt his abilities while attempting it again. So long as you know that each of you can trust the other, you will have a safe and successful ride.
If you have a horse that has been abused, it can be nearly impossible to gain the horses trust. You should not be demoralized, however. Patience and love has been known to work with many horses.
One good method to get close to a horse that has been mistreated is to spend time just chatting and being in his presence. Speak in a mellow and steady tone and carry treats with you. Don't try to ride him and definitely don't ask him to do anything he doesn't want to do. It could take days before he is afraid at the very sight of you. You can try to move closer to him if he is not bothered by your presence. A frightened horse is a very dangerous animal, so be sure that you do not corner him. Offer him a treat and try to stroke his muzzle. You will know that you are making headway when he is willing to take the treat from your palms!
If you can touch your horse and he lets you pat him, you are nearly there. Do not attempt to get on a horse that has been mistreated previously without the supervision of professional trainers who are skilled with dealing with such horses. You do not want to get on the back of a horse who will trust you on the ground, but utterly lose faith once you are on his back.