Timing is essential when speaking in public. The cliche: It is not what you say but more on how you say it, applies so much to public speaking. 

Where you put your pauses during your presentation is one of the important aspects of maintaining an audience that is free from drowsing off. Couple this with humor and you are definitely on a roll.

Timing is the element involved during reactions that are spontaneous especially on developments during your delivery that are unexpectedly expected.

Do not forget, though, that when you expect any laughter to burst any time soon, avoid speaking as your voice and whatever it is that you are saying will most probably be drowned out by the noise of the audience. 

Make sure to remember that laughter is extremely difficult to get and so very much easy to discourage. Try as much as possible to maintain eye contact with the audience for a little time longer when you deliver that punch line. 

The audience size could also affect the way you use your timing. When the audience is small, the presentation you have will most probably be delivered in a lesser time compared to if you have a large audience. The reaction of a large audience will get to be a little longer and not as quick as if the audience is small. You also have to wait until the seemingly ripple effect of your punch line gets to that audience in the back row. 

Believe it or not, putting that much needed silence in your presentation is one of the hallmarks of a skilled and good presenter. No public speaker should jabber constantly away in the hopes of keeping an audience glued to anything it is you have to say. Ironically, this is one effective way to keep their focus off you. The use of silence adds that much needed polish in your presentation making you appear as a confident expert.

Short pauses are effective to use in order for you to separate your thoughts. These pauses last from half a second to two. You do not have to literally count though, just keep in mind to slow down. This gives the audience a chance to absorb all of what it is you are getting across. It also helps if you change the inflection in your voice during the end of a thought as this could also signal to the audience that another thought is coming their way. Pauses are also an effective means if you want to highlight something. Put it before any word or thought you want the audience to focus on, they will most definitely get that.