1. For everything you prune, the first thing you need to do is to set a "goal" for the tree.
Where do you want it to grow? What do you want it to look like today when you are done? Next year? How much fruit/ cleanup do you want from it? etc.
2. Assess potential problems: Are there power lines above the tree that it could grow into soon? Is the tree touching any power lines currently? (If so get professional help, some trees that hold lots of water are great electrical conductors and could give you a nice shock!) Is it headed towards a fence/ house/ roof/ too close to a sidewalk, etc.? Are there crossing limbs/ branches?
3. These factors will determine what you do with your pruning, so once you have assessed the situation.... go for it! Start making some cuts... but remember some important things..
4. Trees don't heal... they seal. You will often see the results of poor pruning when a tree struggles to seal off an improper cut. The desire is a perfect circle exposure. The more oval shaped the cut, the more surface area, and therefore the more energy required to seal the wound. So when you make your cuts, angle your loppers, saw, etc. so that the blades are perpendicular to the stem or branch. If you see a donut shape overcoming your cut in the next year or two... nicely done! You have made a quality cut.
5. Keep your cuts close to a lateral. There is what is called a bark branch ridge on every new branch. Your cuts need to be just outside of the ridge and as close as possible. A tree is full of starches (energy) to keep the tree growing. When you make a cut, all of the energy that was being sent to the cut branch now can be used elsewhere! If you leave a long stub, the starch will continue to shoot down the stub and it will be wasted. If the cut is close to the lateral branch, it will thrive and receive the extra energy you want it to gain.
6. Step back after 5-10 cuttings. It's really easy to get excited and make lots of cuts, but if you don't step back and see the big picture, you may be stuck with a gaping hole or unbalanced tree. So be patient and take a few steps back and look at the tree from all angles. If you are unsure about a cut, have someone watch the tree and shake what you will be cutting. They can tell you what it will do to the overall appearance of the tree.
7. Keep moving. Don't get stuck in one spot. Keep moving around and taking cuts from all sides of the tree and it will quickly thin out.
8. If you need it to grow a certain direction, cut just above a bud facing the direction you would like it to grow. The burst of energy will force the bud to shoot.
9. If it's too tall, use the rule of 3rds. Although many of us were fans of the flat top back in the 90's, it's not a good look for a tree. Pull back 1/3 of the taller limbs 1/3 of the way. Another 1/3 pull back 2/3 and the last 1/3 you can remove.
10. Every tree is a bit different. You have a different goal for each tree and they will each respond according to your actions. Keep fruit trees, for example, open in the middle, they like to branch out with an open center.
Tree care is a long term, low intensity process. Be patient and be smart about your pruning. Quality pruning will give you a well balanced and quality tree or shrub, and maybe you'll enjoy it now, maybe next year!