Self dicipline was the hardest part for climbing for me.
Find the largest mountain you can and just focus on your pedaling and breathing, once you have a good technique then you can push it. When I started road biking I wouldnt even make it to the top of the mountain I trained on, the hardest thing for me was the mental aspect of hill climbing, the unbarable slowness of it so training like that was very helpful. Once I got a good technique and was able to tollerate spending an hour going at below walking pace I was ready to push my self physically.
Training your core muscle may be the most beneficial weight training you can do for hill climbing.