You'll need know, or at least be able to figure out, the names of the notes on the 6 string tab. You can use your knowledge of intervals to do this, saves you remembering everything, there's just too much if you're not using them regularly. There's also a simple method that uses all of the natural notes, the notes in the C major scale.
The image here gives you the note names of the first 5 frets. The trick now is to recognise the patterns so you can find the rest of them yourself!
The natural notes
Notice firstly that most of the natural notes (no sharps or flats) are two frets apart, the exceptions are E/F and B/C. That's all you need to know to figure out the rest. Unless you're on and E or a B, the next natural note is two frets away. Easy.
Sharps and flats
Notes that aren't on this diagram have to be named as well and we do that using sharp (#) and flat (b) symbols. The # symbol means the note is one fret higher than the letter name and the b means that it's one fret lower. So the note between G and A can be called either G# or Ab depending on the key you're in. The note between C and D will be either C# or Dd again depending on the key.
Next
Now see if you can figure out the rest!