How do I trim an evergreen tree?

I am a total garden novice...I have various lovely bushes and trees left in a good condition by the previous owners of our house and I have no real idea how to cut them. I'm pretty sure I can cope with the bushes, they just need to be shaped and trimmed. However I have two large trees that have obviously not been trimmed or cut for some time. Being useless in the garden I have no idea what type of evergreen they are. But I'm worried that if I cut them wrong I will kill them. Are there any hints of tips anybody can give me as to how to do this correctly? Any advice would be brilliant! Thanks for reading my rambles! Mc

 

some pics would be good as there are so many evergreen trees, and each need to be treated in different ways.

 

Specimen conifers generally don t usually need much more than a quick tidy up, don t cut them back into the brown as they wont recover well , if at all ........ conifers used in hedging need the tops trimmed to keep them bushy and tidy
Holly can be trimmed to a nice shape, and again usually the top is trimmed bck to promote bushiness rather than "leginess"
other evergreens are rhododendrons, they are not to be pruned at this time of year as they are in bud
It is not always necessary to trim or prune trees, are they getting too big, or straggly?

 

Whatever you do, don't just trim them regardless, as if they're conifers, unless yews, you could end up with brown dead trees!! :eek:
Photos would be really useful - if you follow the instructions on putting pics into your posts, you'll manage!! Good luck!