Many of the questions asked these days has to do with tree-trimming. Evergreens in particular are challenging. One question we had was in regards to Colorad Blue Spruce. Our reply was as follows...
Thanks for asking about the pruning Blue Spruce. Pruning is pretty easy, and the results can be very pleasing. Evergreens are often more challenging, like where to begin... Years ago in northern Idaho, there was a very interesting Blue that had been trimmed regularly for years. It was a very tight solid cone shape. It was a solid blue all around, very nice...How to start with your trimming depending on the current shape of the tree, and what you need it to do... If there are wide spreading, broken/dead branches, or hanging over the neighbors fence, then that part of the trimming is pretty simple. But if just sitting in the open, no major deformities, then pruning to-shape can be done conservatively. It all depends on the shape and the need.
For example... say the lower branches were hanging over the fence, or, they were broken (as from a storm), or just not alive. You cust these back, or all the way from the trunk. If you cut back to the trunk, make the cut as cleanly against the trunk as practical. This will heal-over naturally faster. Now when cutting branches, as the weight pulls the branch down, it can tear along the trunk. To prevent this, make an under-cut near the trunk, about 1/4 the thickness of the branch or 1/2-inch (whichever is greater). then make you top-cut a bit further out than the under-cut. As the weight of the branch pulls down and starts to rip/break, the under-cut should stop or limit any damage to the trunk. In this manner, even larger undesirable branches can be removed from most any tree. Use a tree-paint to seal the exposed wood. This will help prevent insects and disease problems. 
To do more of shaping versus major trimming, just cut back some of the growth, the leaders (or main outward shoots), but leave the smaller side shoots. This will help direct growth from outwards, to the sides. This will start to fill in the air-spaces between the branches. Once or twice a season, as new growth comes out, cutting the leader-shoots will change the shape of the tree. This works best with smaller trees naturally, but with a ladder, even larger trees can be trimmed-to-shape somewhat. The larger the tree, the more difficult and maybe impractical this will become... And for creating shapes, like animals, topiary, and such, it comes down to small trimmings of the lead shoots that will help create the shape desired. Never top the trees unless you have an absolute need (like a power line overhead), and keep the lower branches. Lower branches adds growth to the trunk, and until the tree is large enough to be strong and a desired size, then leaving the lower branches is desireable. When the tree is larger, and in perhaps a lawn setting, removing the lower branches, making a clear trunk, can be very nice, and functional (like getting the mower around the tree).
Just with trimming, go conservatively, and cuts larger than half-inch or so, put a tree-paint (or any sealant) to cover the wound. That will help preclude bugs and diseases. Keep the tree watered and fertilized, especially during the dry summer months.
Hope that helps...
