It's hard to illustrate some drills without the use of a video... Hmm but here are a couple of simple exercises to start off with!
Start from the baseline, do a jump smash and move forward(shall not go in depth about the footwork technique) and net with the master foot in front of the service line, return to baseline and smash and that's one repetition.
You could do time based ( for example 1 minute active, 45 Seconds rest 3 sets)
Or number based ( 10 reps, but do it as fast as you can, 3 sets)
A simple side to side defend training would be putting shuttles on one side, for example 10 shuttles, then what you hav to do is to bring the shuttle for left to right or vice versa, and that's one set, 3 sets maybe?
There's lots more you can try out but this should get you started at least!