What strategies do you use for novice lifters that struggle to get their depth in the back squat?
There is a minority of novice lifters who can hit depth nicely from day one. The rest have to work for it.
If a new trainee is not getting desired depth then I typically encourage consistency at whatever depth they can achieve and focus on pushing out the knees. Put the time in, get used to the positions, let the body adapt. This is primary.
It can also be useful to have them spend time doing kettlebell squats and goblet squats with lots of time spent in the bottom forcing out knees with elbows.
Squat stance width can be a useful variable. A width that allows them to squat deeper can later be adjusted to a more efficient stance as far as force production goes. Have the lifter play with stance and observe closely. Take notes for later sessions.
If the new lifter does not have good squat shoes then having them put some micro plates under their heels can help once they are comfortable and balanced with regular squatting in their regular shoes. Let them just get used to squatting first.
Have them do the Agile 8 or another appropriate hip mobility sequence during the warm-up every session. For better results encourage them to do this on their own time as well. Keep the sequence brief and simple so that they are more likely to actually do it when no one else is enforcing discipline.
Best thing of all though has just been to have them squat to their best depth consistently and usually it will come.