(Sorry, many pictures take your time! m(_ _)m )
[Basic Style]
- Playing Stance-
You should stand straight and spread your steps outward as the breadth of your shoulders or more.The end-pin is located about 30 cm in front of your left big toe.@Your both big toes and end-pin make a right-angled triangle.The right side of instrument's back shoulder is touched with your left waist bone, and the back right edge of the instrument is touch with inside of your left knee. That time, the bridge top is toward right slantwise ahead such as at 1 o'clock direction. You should image a yellow triangular pyramid of the picture which is made up of the touching point of your left waist bone and the previous triangle. And you should try to keep the triangular pyramid also when you release your left hand from the neck.
The point of this style is that your left hand can be free. The length of the end-pin is adjusted as the height of the saddle (top of the strings or the top of the black fingerboard) is 2 or 3 cm higher than your eyebrow. If you have smaller body than I, the end-pin should be located a little further and the instrument should be inclined.
- How the bow is to be held-
It is like the chopsticks holding style. You should hold the chopsticks ordinarily (as Japanese (^^;). Then remove the upper chopstick and  by left hand, change the position of the lower chopstick from middle-ring finger to fore-middle finger. You should hold the bow as this way. Your little finger is lightly touching with the silver plate clasping the hair. This way is OK. The important thing is you should keep your fingers round inside except the thumb. And you should have space between the right side of frog (black part of bow clasping the hair) and your palm. In the up-bow, your palm is lightly touching with the frog. The top of your thumb is touching with your fore finger, but you should not grasp firmly the bow with your thumb and fore fingers. Please practice up- and down-bow as the above three pictures.
In particular, at the tip and frog of the bow, the actual motion is not so over but you should try to overact like a preparative stretch for exercise within no slip occurrence of fingers.
In drawing the bow up and down, you should not move with fingers, should move with your wrist (and your right elbow also) as the arrow of the above pictures.

- How the strings are to be pressed-

In case of the double bass, the signs for the fingers are similar to other string instruments as fore finger ; (1), middle finger ; (2), ring finger ; (3) and little finger ; (4). An interval of one-half tone is lying between the (1) and (2) and (2) and (4) fingers at the lower position because this instrument has very long string length. The (3) finger serves as support to the weak (4) finger. For the purpose of transmitting the force to the tip of your fingers, you should keep your fingers to round, and your thumb should be located slightly upper point of the opposite to your middle finger. 
At this time, you should pay attention to the line is made up of your middle finger, wrist and elbow. The line is straight at the side view, and it is gently curved at the top view.
- How the strings are to be pressed (Intermediate position) -
Because the position is getting higher (tones are higher), your thumb is moved towards the left side of the neck instead of placed along the middle of the back of the neck. This position starts from the "F" on the G string with (2) finger. In general, the (3) finger is used instead of (4) finger from this position on. The checking point is your supporting style. Is your instrument stable when you release your left hand from the neck? (as "Playing Stance" described at the beginning of this page) You should pay attention to keep the instrument stably when the position is moved higher.
- How the strings are to be pressed (Thumb position)-
When the position is moved higher than "G", one octave higher than the open "G", on the G string, you begin to press the string with your thumb. The sign for the thumb is indicated as "a circle with a vertical short line at the top" (as shone below).
The playing stance at the thumb position is same as basic style and style at the intermediate position. You should bend your body forward slightly, and lightly touch your left shoulder with the neck for stably. Please try to find your own style that you can smoothly change positions with minimum action of your body from the low position to the thumb position without moving the instrument.

At the low position, there is only one (1)-(2)-(4) fingering. But at the thumb position, there are three fingerings as shown the above. Basically you should arrange your fingers as these three patterns accordingly the intervals. You should pay attention to keep your all fingers roundly at any fingerings. And the important thing is the position of your left wrist. The position should be slightly downward to keep your weak and short (3) finger roundly. You should check to revolve your left wrist whether the pressure (weight) is distributed to the tips of your fingers evenly when you press your left palm to the fingerboard with your whole arm.

"Chromatic Position"
"Semi-Chromatic Position"
"Diatonic Position"
At the thumb position, unconsciously, the power is concentrated on your left palm and tips of your fingers since you are conscious to press the strings. But you should pay attention to transmit the weight of whole arm (from your shoulder to tips of fingers) to the tips of your four fingers evenly. As shown the picture, you should press the strings with an image of loading your whole arm on the fingerboard (neck) to the yellow arrow's direction. It is similar to the right hand holding the bow. You should transmit the weight of whole arm to the bow on the string with this image.

[Key Point]
You should keep your left fingers roundly as a gentle arch at any positions (low or thumb position). And your wrist is drawn the similar arch.
The arch is the most effective form to transmit the power and weight to the tips of your fingers.

[to be continued]