Learn to understand your mouse/your mice.
Quick list of some of the mouse's behavior!
Ears pinned, rigid body - This mouse is either scared or angry. Based on the situation and the body language, you can determine which of these two. A mouse can also add ears back when it is sick, so watch for signs of disease.
Ears pricked up, eyes wide open - This mouse is curious and check out his surroundings. It could approach a new friend or a new toy, for example.
Preening or yawning - This mouse feels comfortable. Confident and know their surroundings well. If a mouse you never handle before, sits in your hand and begin to groom themselves, you have found a relaxed little friend!
However, be sure that the trimming is not too strong, then this means nothing more than a casual mouse. (See below.)
Powerful cleaning - This mouse is nervous. Either the mouse is not tame, and has been handled too much or it has been placed in a foreign environment with unfamiliar cage mates. Peace and quiet for the mouse to unwind at the best solution here.
Whipping tail - This mouse is annoyed or scared. The mouse might had enough of being tried being handled, for example. This can also happen if you try to introduce boys and they feel their territory is threatened. If a male whips its tail when you introduce him to other dogs you should keep an eye on the situation for safety but it does not mean that the mouse will not accept the newcomer / area. A frightened mouse waving lightly while an irritated or angry mouse whip pretty hard and fast repeatedly with small breaks between flogging area.
Standing on its hind legs - This mouse is either ready to fight, showing his subservience to an aggressor or just curious about something. They may feel an interesting smell or see anything of interest, in this case, swinging the mouse a little or sniffing around in the air.
Signs of fights is most common among males. When a mouse to show that it is subservient to the will to stand up and put both front paws in front of him defensively. The mouse does not necessarily have to be under attack to show inferiority, it can take the position spontaneously when a dominant mouse goes past, to show that it knows its place in the hierarchy and will not challenge the dominant mouse.
Rider - This is a way for the dominant mouse to show dominance over the mouse riding on. The submissive mouse is not damaged, and sounds is usually the dominant mouse do this without resistance. In a flock of males is unfortunately ridandet a negative action that stressed mice, and can lead to trouble. Males should then parted.
Chasing - Another way to show dominance and may also claim territory. The mouse chasing (the incumbent) can "hold on" in the mouse in front of his mouth / teeth in the back, near the tail. You can see that this has happened through a small wet spot where the fur is wet with saliva. Sometimes even the dominant mouse bite severe damage to the submissive butt. This is more common among males. The slightest sign of teeth gone through the fur and the males have parted.
Preening each other - this can be a sign of several things. Usually to show friendship, but can also be to show the dominance. This can also switch to barbering on the mouse in question is very dominant.
Text and photo: M. Löfgren
Source: http://www.fancymice.info/behaviour.htm (site is no longer active) and Grodan