String Slides
String slides are achieved by playing a fretted note, then whilst keeping a light pressure on the string, push your finger up or down the string and take the note with you. If you squeeze too tight in the process you will get a lumpy one-by-one sound as you jam in the frets in passing.
You want it to sound and feel like ice-skating the strings, not driving a JCB.
The key to keeping your note ringing is to push your finger along the string at an angle similar to pushing a broom, tilted rather than upright. If your finger is at 90 degrees upright _|_ you can only really drag the finger and it can get caught behind fret bars and you lose your aim. Sliding downwards tends to lose volume from your string due to the physics involved, so only use them briefly or with gain (overdrive) for sustain.
String slides can be used with various different styles, for example forcing a fast slide the instant the string is played can give a fast and whizzy attitude to your music whereas perfoming the slide at the end of the note's time can give a more casual groove in joining notes together.