Connect the cassette deck into the output of the DJ mixer. Do a test record to make sure your mix will be recorded and adjust the volume levels so your mix doesn't end up sounding over-modulated or distorted.
Decide if your mix is intended as a demo or for entertainment. So you can plan which songs to use in your set. If you are just starting out in the industry, you might want to write down and arrange the songs you plan to use in your mix. Most professionals or seasoned DJs ad lib and program as they go.
Mix your music to the best of your ability and end with an effect or fade the record out before the tape cuts you off.
Create a label for your mix or write your name, phone number, and email so that the station or club manager can easily contact you if they like what they hear.
Make copies of your mix if you have a dual cassette deck. You can use your mixtape to promote yourself for other gigs or just to get your name out there.