Originally Posted by: smpellz

When practicing and playing scales how do I know which fingers to use?

[/quote]

The goal of any guitar fingering should be efficient & natural motion that helps you play the music you are working on. The default standard is one finger per fret. The only reason to deviate from that standard is if the musical passage you are working on could be played more efficiently by using a different fingering.

[quote=smpellz]For example when playing pattern one in the A pentatonic minor scale what fingers do I use on the D string? Fingers 1 and 3 or fingers 1 and 4?

It depends on where are you playing it. If you are playing this pattern in the lower register, then following the one finger per fret standard, use your index & pinky finger since the notes on the D string are 3 frets apart.

|---------------------------3-5----|

|----------------------3-5---------|

|-----------------2-5--------------|

|------------2-5-------------------|

|-------3-5------------------------|

|--3-5-----------------------------|

But if you playing the same pattern an octave higher, then it's probably easier to use your index & ring. This is an example of an exception to the one finger per fret standard.

|---------------------------------------------15-17--|

|------------------------------------15-17-----------|

|----------------------------14-17-------------------|

|--------------------14-17---------------------------|

|-----------15-17------------------------------------|

|--15-17---------------------------------------------|

This tutorial is a series of exercises aimed at playing all 5 minor pentatonic patterns systematically.

https://www.guitartricks.com/tutorial.php?input=185

Hope that helps!