Clean, crisp articulation is your basic, default articulation, which you can vary for infinite variety depending on your musical needs. Mastering basic articulation is a two-step process and it is important not to jump to step two early. A video presentation of some of this information is here.
"Tip of the tongue to the tip of the reed" is what you'll often hear, though some people don't really mean it. I do. In basic articulation, you also stop the note with your tongue most of the time (sounds like "Tot"), and blow against it, maintaining constant pressure from your diaphragm.
In the following video clip, please notice several things. First, for tone, notice how high my tongue is in my mouth and how forward and close to the ridge of bone behind the teeth. This is to place the tongue in the "sh" position for fast air, and a beautiful, shimmering tone. "Sh" position also keeps the tip of the tongue near the tip of the reed so you don't have to move far, as well as anchoring the sides of the tongue on the sides of the teeth so you only need to flex the tip of the tongue to articulate, rather than move the entire tongue each time. More on tongue position here.
Second, notice that my tongue hits the TIP of the reed AND mouthpiece each time, and it STAYS there for staccato while I blow against my tongue which is closing off the mouthpiece/reed. Notice the movement of the reed, and its vibrations when air moves through it. Also notice that for long notes and legato that the tongue returns to its "long tone" position. This is not something to focus on and try to duplicate, but just a natural occourance.
Staccato, Staccato, Legato (WMV file)
Basic staccato articulation has five steps
1 - Tongue on reed
2 - Blow (against tongue)
3 - Tongue off of reed (now sound)
4 - Tongue back on reed
5 - Stop blowing
You can see in the steps above that the note begins when you move your tongue OFF of the reed. This means that what we think of as an attack is really a release. Don't give an extra pulse of air when you release the reed, unless you want an accent. For non-staccato and longer notes, use an "air release," not a "tongue stop." In other words, do steps 1, 2, 3, then 5. Air releasing shorter notes is a more advanced articulation technique - sounds like "Tah." It is effective for isolated short notes, but you must always blow against your tongue before releasing it for the "attack." Don't start any articulations, least of all short notes, with air and no tongue - sounding "Hah." I call these uncontrollable articulations "airballs."
Tongue-stopped short notes can sound harsh, heavy, or "pecky" without this added technique: Tongue towards the corner of your reed instead of in the center. To practice this, put your tongue on the corner of the reed only and try the five steps above. You may need to move the mouthpiece off-center in your mouth in order to put your tongue here. You will see that in step 2, the reed will vibrate as SOME air goes through the corner that your tongue is not touching. As you alternate between steps 3 and 4, in imitation of short notes, you will hear "zzzzahzzzahzzzahzzz." Now place your tongue halfway between the corner of the reed and the center. Step 2 should yield no sound now, but when you reach step 4, the reed will continue to vibrate for a split-second, giving you "Ping." It sounds like your own built-in reverb. Experiment with placing your tongue in different places between the corner and center of the reed to find the position that is best for you and achieves the best "Ping" sound for your articulation. Make this your default, standard, staccato articulation, and alter it as needed for musical reasons.
Speed Advice on how to speed up your articulation is in my "Advanced Daily Warm-up" here.