Sensory Self-Soothe

Warning

this skill takes a while of consistent work to train your body to have the response you want.
you can then use this response to override what your body wants to do (waking yourself up when tired or trying to relax while anxious), but each time you do this it weakens the association a little
the best thing to do is to just integrate these sensory environments into your daily routine so that you're practicing the skill regularly just by existing in your waking and sleeping environments

The primary concept here is using Classical Conditioning to create an association in your mind and body between sensory input and an emotional state. You're essentially going to train your body like a dog to move towards different emotional states depending on the external cues you give it. So for instance you'd probably want to train your body to calm itself as you turn the lights down. The biggest difference between you and a dog is that you get to choose what you want to be trained to do. And you really do get to choose a lot about this! What you actually wind up choosing for each emotional state and sense is a highly personal choice. That's why I figured I would try to give you as many options as possible and leave the rest up to you!

My strategy was to decide on a full set of sensory triggers for two basic desirable emotional states: Rest / Sleep and Alert / Focused. These can take a while to train your body to do, so pick things that will be easy for you to do, set up your space to make it as easy as possible to keep doing them, and keep at it. The most important thing is consistency and routine. Here are some things I've tried and liked as well as some things I've heard of others succeeding with:

Rest / Sleep

Sight

usually red-yellow spectrum light, and much lower brightness around bedtime.
You can turn on a red-shift filter for most electronic devices these days
LED bulbs also often come in a yellow-orange incandescent style color (and a lot of hobby/makeup lights have multiple color settings for this reason as well, white for when you’re working, orange/yellow for resting/relaxing).
If you're a "smart home" kinda person, you can probably program your lights to automatically shift to red and dim in the evenings.

Sound

some people listen to soothing music
I conditioned myself to fall asleep to the sound of a raging thunderstorm because I sleep during the day and work at night, and the thunderstorm sounds easily block out daytime noises.
A lot of people actually fall asleep in front of the TV, which isn't the best option in terms of light pollution, but is a great example of how sometimes something unconventional just works for somebody.

Smell

Essential oils are actually really good for training pavlovian responses in yourself because of how powerful scent memory is.
You could also use a specific lotion or wash your sheets in a specific scented detergent.
A lot of people say they find lavender scents to be particularly soothing, but again, the exact sensory trigger isn’t important as much as you picking one to use consistently.

Taste

Herbal tea is my biggest recommendation here
you could also go with a small snack/sweet as part of your nightly routine

Touch

A lot of people like weighted blankets or wear a compression garment to bed. My only warning on that is that you should never use these items for someone who doesn't have the physical strength/coordination to get out of or out from under the weight or compression on their own, as it could impair breathing.

Alert / Focused