When I lost my mother there was no way on earth that I could have written a shopping list never mind poems for funeral tributes. A lot of people choose to read passages from the Bible rather than a poem because they think that this is more appropriate.
My feelings are that you should go with what feels right for you and what your departed loved one may have wanted. To be given the task of delivering a eulogy is really an honor hence the responsibility of providing a clear and positive picture of the person you will be talking about is in order. Writing down the information will help you to observe the flow of your eulogy.
If you don t have a well known funeral home in your town, then talk to friends and family who can give suggestions. If you are a coworker, you can focus on work-related memories and humorous anecdotes. People should realize through the poem that they lived with a kind soul and great person.
Don't worry if it runs just a bit longer, take a deep breath and try to relax. As hard as it may seem right now, it gets better.