The time it takes for a horse to get used to you can vary upon the horse's temperament, life experiences (if it's been abused it can take ages), - etc. Grooming is often very good. It's pleasant for the horse, and if you find they have an itchy spot they love being scratched. This can really get them to bond as grooming, scratching etc is a herd bonding behaviour horses use. You can also use food, but unless you're having lots of problems bonding with a horse (especially if they've been abused) don't over do it as you don't want them always expecting food. You can even catch the horse and take him/her to some area which has some yummy grass (if they're paddock is a bit sparse and they'd be inclined to want to graze), this can have your horse thinking of you as someone who's thinking 'for' them. (If the horse is well mannerred, and does not pose any threat to your safety) You can also just go out and spend time in the paddock that horse is in. Sitting somewhere reading a book can be good. YOur horse may come over inquisitive as to what you're doing. You can pet him/her, give them a scratch fi that's what they're into etc :). Raking up/bagging horse manure in their paddock can even help in the bonding process, he/she may come over to see what you're doing and just hang around - that's something for the bonding process as your horse get's comfortable with you and you with him/her. If you're not into reading, raking manure or doing something, just sitting in the paddock doing nothing's also fine, you don't have to hdie behind an action/activity to have your horse come by and acknowledge you.
Basically anything that has you nearby your horse can have you bonding with them.