For what it's worth I still get nervous before talking on the mic, especially at very formal gatherings, and you would be surprised at just how many, DJ's, TV Presenters, Singers, Actors etc do get stage fright as well

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Although it sounds strange to you, to hear your own voice over the P.A, in fact it doesn't sound any different to the audience than if you were talking to them in normal conversation.
Just be yourself, and talk normally into the microphone. The thing to work on is to speak confidentally and clearly and try to pace yourself. Speaking too fast will make what you are saying sound garbled, speaking too slow will make you sound like you are addressing a bunch of village idiots

. Pretty soon, with a little time and practice you'll develop your own individual skill and style and that is the most important aspect, don't try to copy anybody else or put on a different voice, it will sound false and make learning the technique a lot more difficult.
Start with the easy stuff first, just introducing tracks, and buffet announcements, you don't have to be a stand up comedian to be a DJ. Once you've built up a bit of confidence, you'll move on from the 'That was..... this is....' routine. Try and include your audience, invite requests, make them feel welcome.
Even if you are having a difficult gig don't take it out on the audience and try and look like you are enjoying yourself, even if it's not going to plan. Don't worry about making mistakes on the Mic, we all do from time to time, but don't draw attention to it, or dwell on it it'll just make it worse - besides making mistakes shows that you are human and not a pre-programmed jukebox

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As you are building up your skills try not speak to fast, if you rush through a mic link, and you'll more likely trip yourself up and make mistakes or mis pronounciations.
Keep key information on the gig, such as the Bride & Grooms' names, Best Man Name etc on a piece of paper on the mixer, so that you can casually glance down if you have a sudden memory blank, but don't write your links down as a speech, otherwise it will sound like you are reading from a script and less natural.
All of this will take some time, don't expect to develop a mic technique overnight just take it one gig at a time.