If the apple is not pruned, it will bear fruit one year and hardly any fruit the next.
If the tree is not pruned regularly, with the apple do not rush to prune everything in one season, spread it out over two or three seasons. The apple does not like too much pruning at once.
It would certainly be good to find out what kind of apple it is, because some varieties bear fruit mainly on long stem branches and others on so-called stem cakes-spur.
Disinfect your tools after each fruit tree with alcohol. I simply dampen a cloth with alcohol and wipe the shears. This prevents the disease from spreading from one plant to another.
Since I don't waste rakia(brandy), I have plenty of it, so I used rakia. Now I'm leaving it for friends, and medical alcohol will do the job.
If you have someone to show you how to prune, that would be a real bonus.
Good luck and we hope for a good harvest.