DON'T have it sticking out of your pocket, as it looks horrible.
7.13 usually occurs when a batter squares to bunt. The runners sees that, and sometimes heads to the races.
Drop the flag to the side of you that the runner originated from. That might come in handy later.
You might not drop one for a month, or might drop it five pitches in a row. $#!+ happenes, but don't jinx yourself by saying it won't.
For those LL umpires that don't carry one, fellas, it's right in the book, and says "shall". Some argue it's protestable if you call it, and don't drop a flag. It's a requirement, guys.
If you do District post season games, you can tell the leagues where it isn't enforced. And those are the same leagues that go two and out. Poor umpiring is usually a reflection of the league as a whole. That's just an observation from an old guy.
When calling 7.13, you're looking for the runner gaining some sort of advantage, not just some kid with a nervous twitch. (By the book vs. with the book)
Those damn red ones from Honig's cost around $10 delivered, and have a tendancy to go home in the pockets of my Junior umpires. Now they get red shop rags with a heavy, metal nut knotted into one end. Cheap and effective.
For the call, you need to wait for all the action to stop, and ball is back at the pitcher. Then you call "TIME!", and state "The runner at (insert base location here) left early", and impose one of the many interesting penalties. Since rule 7.13 is probably the most complicated one in the book, enjoy the fun. My personal favorite is the bases loaded triple, where the
BR gets gready and is thrown out at the plate.