do you or your mates know any dj's currently playing in your area ???
easy way in is to offer to do a 30 min warm up for em .. get your faces known around the area .. managers soon get to know you .. one tip though dont go in and be better than the current dj to start with .. no one likes a smart arse ...

once you have done a few go and take your demo to the managers personally and talk to them about what you can offer. go and see them when its quiet, try to make the demo disc to cover what the places are currently playing and make it a good mixture .. leave a contact number and answer the fone when it rings . and as dave said get on an agencies books ..

dont forget playing to a live audience is alot different to playing to a bedroom wall ...