I have the clipless pedals mastered. Now what about the shifting? Can anyone recommend a cycling book?

Just keep riding - it'll become second nature very quickly

You're not going to find what you need in a book. You have to ride your bike, and experiment with the gears to learn which settings work best for different situations. The general rule is to chose a gear setting that allows you to maintain a cadence between 80 and 100 RPMs.

You should consider a cyclocomputer that displays cadence in addition to speed. Any bike shop can install it for you, although installation isn't very difficult.

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Rodney Dunning

Also, don't think, if you have a 27 speed bike (triple chain ring plus a 9 speed cluster in the back) about how you get through those 27 gears in order. Think about have 3 ranges of 9 speeds. For the "low" range (small ring), it'll probably get you through anything with a moderate to difficult climb. The middle ring, will serve you well on anything from a moderate downhill grade to a moderate uphill grade. The large ring will serve you well on the flats and most anything downhill. That's a starting point, as many people climb quite well on the big ring. Consider your terrain, choose the appropriate chain ring, then use the gears on the back to move through the range. Once you either top or bottom out, change chainring. You'll get it.

Thanks, gives me a better visual!

Wise person!