I also don't get much deep sleep, usually just under the normal range.
Typically deep sleep happens earlier at night, so if you are going to sleep too late or have insomnia before falling asleep, that could interrupt your deep sleep patterns.
REM sleep tends to happen for most people later in the evening/early morning. Sometimes my REM/deep sleep cycles get mixed up because I think my body is compensating for not getting the deep sleep early on, then alternating sleep cycles more than most people early in the morning.
With major insomnia earlier this year, I've tried taking tea, tinctures and other substances before bed. For me, I have allergies, so loratidine (antihistamine) actually was working the best.
Diphenhydramine, Valerian/skullcap, and other substances helped me sleep but didn't improve my deep sleep ratios (sometimes even left me groggier in the mornings.)
Typical advice would be: set an alarm to remind you when to go to bed, have some kind of relaxation technique/rituals before bed, drink tea or something relaxing (herbal tea like chamomile, mint), limit screen time, maybe read or something to quiet the mind. These have helped me fall asleep but haven't necessarily improved my deep sleep though. Sorry, that's pretty generic advice... good luck -_- zzz.
