First of all, Remain Calm.
I know this can be hard since the Backrooms can be a very disturbing and isolating place, but if you keep your sanity levels high, you will be able to survive for longer and avoid making simple mistakes that can cost you your life, or worse.
Finding Food and Water are top priorities, as is finding weapons and medical supplies. Finding other people may be helpful, but remember, Do Not Call Out, unless you know the person you are calling out to is friendly. Loud sounds may also attract hostile entities, so it is important to remain aware of your surroundings.
I see that your last post was 2 hours ago, so you likely still have enough battery to receive this message. Make sure to save your battery at all costs, as access to the internet will allow you to gather useful information when you need it. Only turn on your device when you absolutely need it.
You may also choose to turn on your device to record significant phenomena, entities or locations within the Backrooms, as this information can be useful, if the device is lost, to other Wanderers who discover it. Those who sacrifice their lives mapping out and documenting the backrooms are held as heroes by many, and are greatly respected by the Wanderers of the Backrooms.
Goodluck to yah, let us know if you survive long enough to find some sort of Colony or Outpost.
-The Rayne Wanderer