When you first start a monologue you read it a completely different way than the way you will once you have practiced it. You may be thinking, oh it would be easy, and I thought so too. It definitely could be easy but to make the monologue genuinely sound real and portray great acting you have to do more work than simply just read.
My first difficulty was remembering the words of the monologue but that was the least complex part of actually learning the monologue. You have to literally pretend you are that person. My drama teacher started asking me questions as if I was that person. This may sound simple but it's much harder because you only have so much information on what this character is like but you have the responsibility as an actor to assume what their overall personality is.
You have to get into character, become that character. I did this by relating to the character, I've been in situations that I've had to make excuses for in order to not go. This character is trying to come up with any excuse and carry on with that excuse and won't stop till he get's his way. Then once you've got the swing of that, you can't recite the monologue the same way every time. That was the hardest part for me, it's very hard once you get used to saying something a certain way to change it so it's not too repetitive. Although I progressed a lot within this monologue, it was only the beginning.
The next monologue we started actually focusing on was much more difficult. Although it was much harder it was more interesting for me to portray. I fell in love with this character because I really couldn't relate. She was basically psychotic.. This girl's cat got ran over and to put it simply she decided to keep her cat in her fridge. Now she's complaining how the cat is starting to stink up the fridge and it's time for her to bury Fluffy (her cat) because her cat deserves the very best. In this monologue there were so many different emotions. At first I was sad, then mad at the killer, sad again, and then remembering my cat and how I would honor it. I still have yet to perfect this monologue and I should probably get back to practicing it.
Below I have a few sites where you could find some monologues, if you're interested: