Here I present two ways: One with help of software (very efficient) and one with no need for either a computer or a guitar.
 
The software is the following one, suggested to me by another Gdotcom member:

 
Downloading and installing the program shouldn't take more than seconds on broadband. It's very compact. And it's essentially free.
So instead of me filling long pages of text, I suggest you spend a few hours a week with this program until you know them all.
 
It's essentially the same idea as the following, but way more practical:

 
(DISCLAIMER: a whole bottle of rum is hardly a good idea in general, especially when you need a clear focused mind)
 
You'll realize the program is pretty straight to use. You can isolate and learn the notes per string or per fret or all together. Whichever way you do it, I guarantee you you'll have them down pretty soon.
Practice Tips: A smart way to approach this is to minimize possibilities: If you memorize only the 7 natural notes, the remaining 5 notes are very easy to find.
So, isolate one string at a time (E,A,D,G,B,E), then do them in pairs (EA,DG,BE) then in triplets (EAD,GBE). To make sure you have them down well, then isolate groups of frets: (0-2-3-5, 5-7-8,8-10-12) and practice them across all strings. The frets suggested are not random. They are either "dotted" frets (easy to spot) or consist primarily of natural notes (no sharps/flats). Finally activate all frets and strings. The above procedure contains redundancy in favour of complete beginners. IMPORTANT: try to name the note pointed to you BEFORE even looking at the buttons below to select your answer. The nature of the program and options often causes querry notes to be adjacent and you can reply correctly just by counting steps instead of really recalling what note is there. Cheating like that will only delay your progress.
Once you're able to name quickly any note pointed to you on the fretboard, there is still one little thing to do and it's important. You'll notice that if I ask you to give me all the locations of an "F" (or any other note) you'll probably hesitate a little. In order for your knowledge to be complete and confident you need to do the opposite practice: For each of the 7 natural notes practice quickly finding all its locations on the fretboard.
After you're done with both of these practice routines you're ready to confidently conquer the world of scales and chords.
All in all I think if you dedicate one day you'll master it.
BONUS: Additionally, this program has a section with scales and chords. It is not the most complete but it sure is enough to get you jump-started.
 
 
 
BUT you can practice the notes away from a computer or a guitar:

 
When your mind is idling (ie in the bus, at a red traffic light, while in the shower etc) picture a fretboard with your mind. Restrict yourself to frets 0 through 12.
Now, choose a note and VISUALIZE all the positions yu can find it on the fretboard. if you don't visualize it, you won't be able to recall that knowledge when you hold an actual guitar in your hands. Eye-memory (picture) is much quicker and more efficient than general memory (words). If you have time to choose a second note as well, make it one that is not directly adjacent to the previous one.
Other things you can do, pick a fret and think of which notes are located there. Or pick a string and find which notes are on which frets.
 
The advantage of this is that your knowledge of the notes becomes independent from your finger memory and you save practice time while making something useful out of mentally idle moments.
 
This method,however, has one prerequisite: you have to have understood how a guitar is tuned, how the notes are spaced and how that spacing translates to guitar, in order to be able to find where the notes are. Here's a short review of that knowledge.
Long story short, the natural notes are A_BC_D_EF_G_A in that order and spacing . Every typed character (letter or underscore) represents a semitone.This means A is a whole tone's worth far from B, while B is only a semitone away from C. "_" represent semitones whose note occurs by adding accidentals to the natural ones. The _ between A and B is A# or Bb. The reason I like to show the notes this way is that it helps visualize the notes on the fretboard. Each fret is also worth one semitone. On the 5th (A) string of a guitar the natural notes, in the order mentioned above, will fall on frets 0,2,3,5,7,8,10,12.
 
 
 
 

With good practice you can have it all down in little time!
- RG -