Ah, the million dollar question...

The general principles / options are:
1. Isolated Activation
2. Co-Contraction Activation
3. Functional Activation

Depending on what philospohy school you come from determines what you do.

From Uni QLD, you would go in the order listed - isolate, co-contract, functional integration

I think this is a nice easy way to start - it makes simple sense and rarely will you ruin a patient. However, it is probably the most frustrating because if you can't isolate a lumbar multifidus (LM) contraction, then you are stuffed because you don't progress...

The easiest way to show people what it should feel like is to sit in neutral sitting. Place fingers over lower L/S near Spinous Processes. The lean back maintaining hip flexion angle. Your will feel LM turn OFF. As you come back forward, it will turn on. This is a normal postural activation of LM

Alternatively, you can use a gentle pelvic floor contraction and aim the pull up to the L/S at L5 if you like.

Or ask patient to poke their finger into their back and then try to slowly squeeze it out - quick contraction is likely to be ES aponeurosis.

There are so many ways to do this.

I assume you are in Australia - try to see if a uni library has "therapeutic exercise for lumbopelvic stabilisation" bu Richardson, Hodges and HIdes.

Good luck