Any suggestions how to slide from an open string note? One song I’m learning has a slide from open E to the octave at 12. Do I just pluck, hammer it on the first fret, and slide?
Also, does anybody have a good exercise to improve precision when sliding? I often overshoot or undershoot my target note.
Thanks, friends!
I’d just pluck and slide without hammer-on. That should be good enough.
To improve precision, I find it easiest if I set my eyes on the fret I am sliding to. The same works well if you have to jump up or down the fretboard.
What @Krescht said 
It depends a little on how long time you have for the slide… As long as you pluck the open E and then slide to land on the 12th fret (in time), it doesn’t matter a whole lot were exactly that slide starts.
The more time you have (or need to fill) with the slide, the lower I’d start; if it’s a quick slide, I’d probably start higher (to get to my target in time).
In any case, I wouldn’t worry too much about including all notes/pitches in the slide; I’d probably start in the general area of a “G” 
+1 to what @joergkutter said!
For slides, the important thing is that you do a teeny bit of slide somewhere.
If it’s an open string slide, where you do the slide (what fret you start the slide at) won’t matter.
I was going to type more, but @joergkutter said it all already!
I’m work on the opposite, sliding from the 12 fret to the open string, which is much easier. I’m interested in finding out how best to do it low to high.
It took me a while to get the hang of it. As the responses above said, it really doesn’t matter where you start, just where you end. For the song I was working on when I first posted, the bar goes |0-0-0-0/12-12-12-12|, so the really important thing is just making sure to pluck the last three eighth notes at the same volume as the first four. I’ve found that it helps to already have your fretting hand in motion when you drop the finger onto the string, and concentrate on hitting the target noted precisely.
Hope I’m not saying the obvious here but you also need to consider if it’s a legato or shift slide. In the former you slide up to the target but don’t pluck, in the latter you slide up to the target and then pluck it on the beat.
I did not know that. Glad you mentioned it. Are the two types notated differently in sheet music or tab?
Yes the legato slide is indicated with both the slide line and a curved link between the notes:
Legato first then shift (where you strike the final note). I’m not sure but I think the shift is more common in rock music as it maintains the beat better.
I learnt Fleetwood Mac Man of the World a while back and that uses masses of shift slides!
