• Be Loud and Clear without shouting. Don't let your voice creak while being loud.
• Practise Variation. Variation in your tone can convey your expressions.
• Stress on Powerful Words. You can take effective pauses, stress on a certain set of words, which will help your speech sound more interactive.
• Create a Crowd-Pleasing Speech. Connect with the audience from the start. Use tools like humour, story and experiences to attract the crowd.
• Effective pauses build curiosity in the minds of the people listening to you.
• Avoid Ahs and Uhms. To avoid such fillers, practise speaking a lot.
• Sound Enthusiastic and Confident.  Do not sound lousy, monotonous or use the same variation of tone in your speech. Display enthusiasm in your words.

... in the initial one and a half minute to know whether they are going to listen to him/her any further or not.

This leaves you with a small time span in which you are supposed to grab the attention of the audience.