well i'm not sure what you mean by start but its fairly easy. to find your base interest, PLAY. Lots! observe ask questions. After a few days, you'll see what they're interested in. It could be gross motor, fine-motor, dramatic play, anything really but make sure while your on it they can learn lots of different aspects. I do mine through a bubble graph. Say the middle is "Travel" then it branches off into gross motor (where it will branch off to activities such as walking, any gross motor that teaches travel) then fine motor, then science, dramatic play (airport maybe, or groery store), ect. Document as you go because its harder to prove what is learned and also its a reference point for you to go back on to see what you've taught because it can get lost or you can forget certain things you wouldve like to teach.

get it? lol