Delivering eulogy speeches is quite possibly the most nerve-wracking public speaking engagement one can ever hope to get. While some look upon them as a chore or perhaps, an unnecessary waste of time and effort, you'll be surprised to note that eulogy speeches are purposeful for a variety of reasons.
A eulogy is not meant to be a summary of a person's life nor is it meant to encapsulate every single experience that the deceased has ever had. And furthermore, a eulogy speech should never 'speak for everyone present'. In fact, the main purpose of a eulogy is to express just how much meaning the deceased brought to the lives of those he knew.
The best eulogies, or rather the most effective ones are usually those that come straight from the heart. These will usually indicate all the joy and love that the deceased brought to the people in his life, especially yours (assuming you are delivering the eulogy). It does not have to be perfect and does not need to recount every single achievement in his life. What it should do is capture the essence of the man, what he stood for, what he believed in, the principles by which he chose to live his life, and even the sacrifices he may have made for his family and friends.
If you have been asked to deliver a eulogy for a friend, it may also help if you mentioned just how good a friend the deceased was to you. No need to go into the long and boring details of the friendship (like how you met etc) but instead, focus on how he was always there for you especially when you needed him most. One or two such examples will do.
Remember you may not be the only one speaking at the funeral, so keep it short. Select the most meaningful experiences you shared with him and deliver your speech well. You may be overcome with emotion especially as you begin to drudge up painful memories. Sobbing uncontrollably in the middle of your speech will just make it that much harder for the family. So, remember to keep your composure. Also, just in case you lose your train of thought, you may consider having small notes handy.
No matter what happens while you're delivering the eulogy, remember that the family appreciates just how difficult it must be for you to speak at your friend's funeral. So, there's no need to ask everyone how you did. Stay positive throughout your delivery. Even if the deceased had personal demons to battle, there's really no need to bring up his painful past unless it is to simply say, "John led a tough life but he was the most optimistic and pleasant man I had ever met. I often asked him how he could stay so positive despite the hardships that faced him, but he just laughed them off as simply being a part of life's great challenges." That would certainly speak highly of your friend and of yourself.