PSkim is, as usual, correct. The only difference I have with his technique is using the nail of the thumb on glissandi that move toward the body (i.e. right hand moving from higher register to lower register, or left hand moving from lower register to higher register).
The reason using the nails is better than using the skin of your fingers is because the gliss will be more even.
There is absolutely no reason for anyone to draw blood when playing any kind of gliss, if they practice it correctly and carefully.
There are several ways to practice glissandi, and one of them is as follows:
1) Start with your hand in position at the beginning note, but do not depress any keys. "Play" the gliss by sliding your hand up or down the keyboard, but do not depress the keys. It should feel light, you should be gliding your hand and your nails should be making an even clicking sound as you go from the starting note to the ending note. What this does is reinforces the proper movement and speed, and practices beginning and ending on the correct note in time, so make sure you end on the right key.
2) The next step is to depress the first note, make the gliss movement but do not play the other notes until you get to the last note of the gliss, which you should depress. In other words, it's the same as step one, but you sound the fist and last notes only of the gliss.
An intermediate step - if you are having trouble with this - might be to sound the first note only - with the entire gliss movement, practice that until it is comfortable, then sound the last note only - with the entire gliss movement, and finally sound the first and last notes with the rest of the notes silent.
2) The final step is to play the first and last notes of the gliss, and each time you practice it depress the middle notes more and more. At first a few of the notes might sound, and later more notes might sound. What you are trying to establish is the proper depth you need to depress the keys in order for all the notes to sound.
Note the key does not have to be depressed all the way to the keybed for all the notes of a glissando to sound, and if you try to play a gliss by depressing the keys all the way, you could end up drawing blood. On any piano there is a point before the bottom of the key where the note will sound, and finding that is important in playing a glissando without hurting your hands.
The disadvantages of hurting your hands by playing glissandi improperly are 1) It causes pain, which will cause tension, which will translate into tension in other parts of your playing. 2) Because of pain and injury, you may not be able to practice the gliss with the repetition necessary to master the passage in question.
Topic: Glissando...