The easiest way to remember lines, is to highlight each paragraph in a different colour. Learn and perfect one paragraph at a time. Once you have learnt your lines off by heart, add expression to your monologue. Emphasis on important points is important, to get your message across to the audience. Add facial expression and gesture only once you have mastered saying your monologue in character, with expression and emphasis. It is very important that the tone and mood of the monologue is not lost. These two important aspects are created using your voice and body language. Decide how you are going to block your monologue. Are you sitting throughout the monologue? Are you standing? Is there a need to pace or walk about? Who are you speaking to? Where is this person? 

Take note of the above in your preparation process.

Good Luck!