You can start learning to play on either an acoustic guitar or an electric guitar. It depends what you want to play. Some think that it's best always to start on acoustic then 'move on' to electric. However, if you are only really interested in electric guitar styles then you might as well start the way you mean to go on - so get an electric guitar.
Of course, a lot of the basic techniques are the same whatever type of guitar you play.
It's probably fair to say that you can get going on guitar more quickly than almost any other instrument. With just three or four chords and a basic strumming technique you can play along to quite a few songs. However, if you want to keep up your interest and avoid getting into a rut then acquiring a good knowledge of scales, arpeggios and chords will give you a fresh challenge and a much wider range of techniques and ideas to tap into. These techniques will open up endless possibilities and really make a big difference to your playing.
Fingerpicking or plectrum (pick)
There are two main ways of playing the guitar - using a plectrum (pick) to pluck the strings or using your fingers (fingerpicking).Playing with a plectrum enables very fast playing and gives quite a hard attack to the note. Fingers (or finger nails) give a softer attack and have the advantage of enabling several notes to be played at once that are not necessarily on adjacent strings.
Classical guitar is always played fingerpicking style. Blues, jazz and folk can be played with fingers or plectrum, depending on the style you prefer and the type of music being played.
I usually encourage beginners to learn both styles. My comments about piano technique apply to the guitar too. To really get to know your instrument, some classical pieces will do wonders for your technique and knowledge of the fretboard.
Standard musical notation or tab
Many non-classical guitarists find tab very useful. You don't need to be able to read conventional music - tab shows you the fret and string to play. You don't even need to know what notes you're playing (Eb, F# etc). The disadvantage of tab is that is doesn't show the rhythm (although some forms of tab do add conventional rhythm symbols to the fret numbers - of course this does require that you understand conventional rhythm notation). So tab users do need to be familiar with the piece of music they're learning otherwise there's no way of knowing how the rhythm goes.
Classical guitar music has always been written in standard musical notation, with a few additional numbers and symbols that relate specifically to the guitar. In recent years, it has become quite common to find guitar music written in both standard notation and tab - one written above the other - so you can use whichever you find most convenient.
My approach to guitar teaching
As a fan of classical, jazz and blues music these are the styles I focus on. Of course a lot of basic techniques are the same whatever style you want to learn.
If you just see playing the guitar as a fairly easy way to accompany yourself singing folk or country music that's fine. My main interest, however, lies in the guitar as an instrument in its own right. I therefore encourage pupils to develop a sound technique and knowledge of the instrument. This involves the following:
• learning the notes on the fretboard (yes, that means all of them - right up the neck!)
• scales - major, minor, pentatonic, common modes (e.g. Mixolydian and Dorian)
• arpeggios - triadic, major 7th, dominant 7th, sixth, minor, minor 7th and diminished
• basic chords - major, minor, 7th, major 7th, minor 7th in various positions on the fretboard
• extended and altered chords e.g. 9, 13, #9, b9, 7b5 etc. (these apply mainly to jazz)
As far as learning chords is concerned, I don't encourage the use of the typical "20,000 chords for Guitar" type of book. At the rate most people learn chords this would probably take them several centuries! It's more important to learn how chords are structured - that way you can start with the basic building blocks and gradually extend your knowledge.
I'm happy for pupils to stick to using tab but I do encourage the learning of standard notation if at all possible.
I use a wide range of exercises and specially arranged pieces to help pupils acquire a sound technique. They become a sort of tool kit that can be applied to the music of your choice. Most people find that as their technique and knowledge increases so does their range of musical interest, opening up ever new musical paths to explore.