Important DSLR tips to keep with me all the time?

I need a list of important tips to write in a note book and keep in my camera bag… Like:
ISO
Shutter
Aperture
and any other important things that could slip my mind(nikon d5100. If it is important)

Added (1). U helped a bit. But i need some techniques and stuff that i should always know and might forget from time to time… Like depth of field and shutter speeds, and burst techniques.stuff like that

It depends on the environment where you will use your camera.
For low lighting, use a high ISO setting, slow shutter speed and a lower aperture value.
And vice-versa.

I would recommend you experiment a bit before you consider going for a serious project/adventure.
And what I would prefer, personally, is to keep the camera on "P" mode. I personally find it most convenient and i only switch to Manual (M mode) when required in some extreme circumstances.

As for any other tips, protect your camera and the lens. Do not take a picture of the sun while directly pointing your camera towards it, keep the strap either tied around your neck or arm, use your elbows as tripod legs while taking photos (rest your elbows against your body when taking a picture, youtube these tips i'd prefer), and most of all, stay creative! Keep thinking out of the box.

Hope this helps.

Never change lenses in a dusty, wet or other problem area…

The tip on changing lenses in the dust is a good one.
But I always run through a bunch of checks before shooting.
Picture Profile
White Balance
ISO
Aperture
Shutter Speed
Exposure Meter
Composition
Focus
Snap!

ISO: Always use the lowest ISO possible. The lower the ISO, the less "noise" in your images.
Shutter and Aperture: These both depend on your situation at the time, and what you are trying to accomplish. If you want to freeze fast-moving subject, you want a fast shutter speed. If you want some blur, slower shutter speed. Aperture, same thing - depends on your situation. If you want a really shallow DOF, keep that aperture wide open. If you want a deep DOF, close that aperture down. These work in conjunction, of course - if you have your aperture wide open at like f1.8 or something, you can get away with a much faster shutter speed, and conversely, if you want a really deep DOF, you might have to use a slower shutter speed, and all this depends on how much light you have. If you have low light, in either case, bring a tripod.

My personal tips: Always have an extra battery, extra cards, and get a carrying strap for your tripod. I know a lot of photographers like to travel light, but I figure it's better to have the equipment and not need it, than need the equipment and not have it. Keep filters on your lenses, sometimes a filter can save your lens if it gets bumped or dropped.

ISO:

The higher the ISO speed, the more light the sensor can pick up. For example, if your camera is set to ISO 800 you can take a well exposed image in a darker room than you could with ISO 100.

More ISO = More noise (unless in dark)
ISO 200-400 outdoors and 400-800 indoors.

Shutter speed:

High shutter speed = Slows down action -light
Lower shutter speed = Blurry images +light

Aperture:

Aperture controls depth of field (Focus and blur in a photo.Bokeh)
Long lens + Shoot close = Bokeh effect (blurred background)

+Aperture = - depth of field
-Aperture = + depth of field

+Aperture = Smaller "hole"
-Aperture = Bigger "hole"