Smearing honey on loads of trees will help increase chance as you can only find them on sweet scented trees. Any tree will work but they only have a very slim chance of appearing as it is.
Try using a quick ball at the start just in case that works for you. If not, Bring a a Pokemon with false swipe if you have it and use it until heracross has 1hp.
Status it with paralyze or make it sleep then ultra ball it (Pack alot of them as he can be a dirtbag to catch.) If it starts to take awhile, use Timer balls to take advantage of this and if it's night, use dusk balls.