As I noted in my post on Hard Apple Cider Basics, you can improve the quality and to increase the potency of your hard cider.
1. Mix together different types of apples. I don't know exactly how this works, but it works. Different apples have different levels of sugar, are more or less tart, etc. So one type of apple balances another.
2. Sanitize everything. Use campden tablets to sanitaize all of your equipment. They can go right into your cider and will kill off any unwanted bacteria or mold. This will also kill off any naturally-occurring yeasts, and so you'll need to add yeast.
3. Use a hydrometer to figure out your potential alcohol. Add the appropriate amount of sugar.
4. Add yeast. I never know what kind of yeast to buy in the brewing supply store. I usually use champagne yeast in cider. I like to start the yeast in a glass of cider. When the glass is nice and foamy I pour it into the rest of the cider.
5. Use a stabilizer when fermentation is done. Available in a brewing supply store. This kills off any remaining yeast and keeps fermentation from starting up again after bottling.
6. Back-sweeten. If all goes well, you cider will taste dry when fermentation is done. You may prefer to drink it sweeter than that. I like to add some brown sugar or honey.
7. Bottle. I collect empty wine bottles from frienda and buy new corks. I've used three different corking tools and here I do find that spending more money makes the job easier.
8. Age. Sometimes the cider tastes great as soon as I bottle it. Sometimes I am less than impressed. Sour or bitter cider generally improves with age.