Engine lugging is basically too little rpm/power to handle to load applied to it. There is more to it, technically, but that is the basic.
The way to avoid it is to use your gearbox to match engine rpm/power to allow you to meet demands. This will also allow you to use a smaller throttle opening.
Anyway, that is my best attempt at describing how to avoid the issue. This is a smaller engine, so you will never go wrong by adding some rpm, via downshifting, when you face a hill or other loaded condition.
Experience is what you need, and you really can't get that through a forum.