Let's say someone asked you to play an F# (F-sharp) note on the guitar. Where would you begin? You know that the guitar strings are tuned to EADGBe, which is standard tuning, but do you know the chromatic scale?
The Chromatic Scale is, what I call, the alphabet of music. It is a scale that consists of 12 notes, each a semitone apart. A semitone, also known as a half step, is the distance of one note to the next adjacent note. Semitones are always one note and one fret apart. An example of a semitone would be:
e|-----| e|-----| e|-------|
B|-----| B|-----| B|-----9-|
G|-----| and G|-----| as well as G|-12----|
D|-----| D|-----| D|-------|
A|-----| A|-2-1-| A|-------|
E|-0-1-| E|-----| E|-------|
When it comes to tabs - to achieve a semitone, you literally add or subtract 1 to whatever note you are fretting. BUT NOT ALWAYS. As you can see in the third example, G|12 and B|9 are semitones but they are on different strings. However, if you tried adding one to the G|12 (12+1=13) you would notice that G|13 is the same note as B|9.
Therefore,
e|-------| e|--------|
B|-----9-| B|--------|
playing G|-12----| is the same as playing G|-12--13-|
D|-------| D|--------|
A|-------| A|--------|
E|-------| E|--------|
Confused? This is where the chromatic scale comes in.
In western music, there are 12 musical pitches. They are:
Ascending
A A# B C C# D D# E F F# G G#
Descending
A Ab G Gb F E Eb D Db C B Bb
# means sharp
b means flat
Whenever one is ascending, sharps are mentioned and whenever one is descending, flats are mentioned.
================================================================
A A# B C C# D D# E F F# G G#
Bb Cb Db Eb Fb Gb Ab
Note: If they are in the same column, they are the same note on guitar. ================================================================
Basically, this scale cycles between every note. Now lets try to find that F# we where looking for earlier.
If you have memorized standard tuning by now, you'd know that the guitar has two E-strings. What comes after E...? F does. Now what's after F on the chromatic scale...? F#. It should be on the second fret of any E-string.
Now find F# on the A-string. If you did it right, it should have been the 9th fret. You can literally memorize the order of the notes in the chromatic scale to find any note you need.
Here's a great chromatic scale exercise to build finger strength, speed, and dexterity. Also a great way to warm up.
e|-----------------------------------------1-2-3-4-|
B|---------------------------------2-3-4-5---------|
G|-------------------------2-3-4-5-----------------|
D|-----------------3-4-5-6-------------------------|
A|---------4-5-6-7---------------------------------|
E|-5-6-7-8-----------------------------------------|
It's important to use all of your fingers (thumbs don't count). Start each string with the index finger and end each string with the little finger. Ascend, descend, repeat. If you are new, take this very slowly and be careful not to push yourself too hard. Focus on sounding the note clearly before going for speed. If you are more experienced, focus on speed and clearly articulate each note.
Try to practice at least 15 minutes everyday.