You may want to start with watching of this VIDEO that is an introduction to grid trading, covers the theory and basic concepts of grid trading, presents couple of basic and popular strategies that grid-traders use.
Grid trading in its pure and basic concept does not work very well. Combined with other methods can be very powerful.

In the Trading Systems Ziemo presented couple of systems ideas that combine various grid trading approaches with harmonic patterns trading:
Harmonic Grid Trading System - Directional Profits

Harmonic Grid Trading System - Reversed Martingale

Harmonic Grid Trading System - Volcano Setup

Harmonic Martingale Entries System