
Originally Posted by
bluesking
This is a very good and serious question. I used to ask it all the time and eventually I forgot about it and realised that (for me at least) it didn't turn out to be relevant.
Here is my reasoning:
It depends on whether you are improvising or playing a set composition.
For a set composition the answer is simple: Learn how to play it, then play it!
For improvisation: use your ears! It's a mistake to think that you should know which fret you want to land on. All you should know is what sound you want to hear in your ear. This leaves you with two options: slide up/down the string untill you get the sound you want or take a general "guess". The latter means there is a fair chance of making a mistake, but more often than not you can turn that mistake into a great feature if your ears and scale knowledge is good.
When improvising, your goal shouldn't be to play "without errors" it should be to "play creatively". This attitude is actually what is necessary to play "without errors" by converting them into features. Unlike in set compositions, there is no "erroneous way" to improvise. From a theory point of view almost every single note can be useful against every single chord in some way or another. Remember there is no such thing as "cheating" when it comes to improvisation so take advantage of mistakes and have no guilt!
So thats all well and good. But pressumably you have to be some sort of uber-mensch to play like this. Perfect ears and abilities to turn mistakes into wonderful works of art. Magic, right? Nope....
Ear training is covered in detail elsewhere on this site, so I'm not going to go into that.
But here are some ideas you might like to try when "guessing" at the right note:
1.) If you are guessing a note which you intend to hit with your 3rd/4th finger, try to err on the side of playing too high... you can always use 1st/2nd fingers to recover by pulling off lower.
2.) If you are guessing a note which you intend to hit with 1st/2nd finger, try to err on the side of playing too low... obviously
3.) If you are just blindly guessing try to use your 2nd or 3rd finger. This gives you maximum ability to go lower/higher.
4.) If you land on a note and simply don't know whether you want to go lower or higher or even where on earth you may be in the scale: BEND!!!!!!!!!!!!!! Bend like crazy. Bend untill the note sounds right (you might have to bend a full major 3rd in some cases so be comfortable with big bends).
5.) Guess at something logical. If you hit a bum note, try to imagine that note as being part of an arpeggio you already know. Hit some others from that arp. Chances are pretty good that you will inadvertently end up playing a nice altered scale pattern. Remember, if what you play has order and familiarity in some way, it will sound deliberate (even if its deliberately tense and odd).
6.) Go chromatic. Like in point 5, when you hit a bum or unkown note repeat a chromatic pattern (e.g. 123, 234, 345, 456...). Eventually you will get to a point where your ear catches up with you (i.e. you have found your bearings in the scale) and you have built up lots of tension.
Nothing magic here, just strategy and practice.
Remember, even the most well-rehearsed guitarist makes occasional mistakes. It's the flexible & brave guitarist with the big ears that can make every mistake seem like a work of genius.