Generally if you suspect ANY head/neck/spinal injury, the casualty MUST NOT be moved ESPECIALLY if they are unconscious but then it's very difficult to tell if there is a head/neck/spinal injury if the casualty can't talk to you unless there are any unnatural angles, lumps or swellings.
Concussion isn't always immediately apparent either - it can set in a lot later. Even if the casualty is upright and talking, you should insist on a visit to A&E for a "check-up from the neck up". Obviously you cannot force them to go if they don't want to but if they collapse 24 hours later with a brain bleed, at least you can say "well I did tell you..."
The biggest thing to be aware of is the onset of shock - this is the biggest killer of the lot, especially in the outdoors, and it needs treating IMMEDIATELY. Symptoms include raised pulse, very dialted pupils, cold and clammy skin even on hot days, talking rapidly and not making much sense, shallow breathing, confusion, dry mouth, nausea, lapsing into unconsciousness and eventually death.
I could go on about this for pages and pages - get yourself booked on ANY first aid course (your local St John Ambulance and British Red Cross offer them regularly) and get a bisic first aid kit and some wound dressings in your pack and you're good to go.
BTW if you do have need of rescue in a remote area (e.g. Mountain Rescue, helicopter extraction, etc.) you should alert the police first - they will arrange for the required services to attend. No good calling an ordianry ambulance if they can't get to you!