Your trees in your yard belong to you, and they are your responsibility. This doesn't mean you should be irresponsible by attempting to trim or remove them all on your own, especially when you are putting those around you or someone else's property at risk. If you have a tree in your yard that needs to be trimmed or removed, the responsible thing to do is to hire a professional to do this work for you.
Do you have a tree that has suddenly died and that needs to be taken out? Have you been making plans to get started on this work within the next week or two? While cutting down a tree has the potential to make you feel like an accomplished lumberjack, the reality is that this is almost certainly going to be something that is best left to professionals. Instead of going out and cutting down the tree yourself, take a moment to consider if it's really the best idea.