all great ideas - **especially** the 2 and 4 metronome beat approach. Can't recommend this enough to give you a really organic feel of time and groove.
I remember when I started doing this and it initially felt quite strange - like when you are in the air while jumping on a trampoline. There's no comforting support for your beat and you kind of hang there by yourself, but then you hit the 2 beat and you are supported again.
Even trying to get the mental 1 beat to start playing feels weird. For this, the technique that Ed Friedland talks about is a good one - tap your hand on your thigh with the beat and when your hand is in the air that's the 1. Start counting at that time and keep it up as you stop tapping and start playing.
Start by playing quarter notes only and do scales and arpeggios. Make sure you do multi-octave scales and watch your timing as you change position - that's the spot where micro-lags in timing will happen and this beat technique will amplify them and show them up. Also focus on giving the notes their full value - this is also harder with this technique but your chops will go through the roof.
Record yourself too - I use GuitarTracks to record via computer and I set up two beats in a drum machine - one with a standard back beat, and the basic 2-4 kick beat. I recorded myself using the basic 2-4 and then dropped it out and played back with the full backbeat. Ouch!!
Once you are happy with your sound using quarter notes, start to mess round with:
- speeding up the beat
- playing eighths/sixteenths/triplets
- playing syncopated rhythms (a nice starting one is SRV's Couldn't Stand The Weather)
- adding various rests etc.
- adding some swing or shuffle
- slapping
I found that I really quickly got used to the feel and it became easy to count myself in without tapping my hand. I also found that once I locked my timing it got easier to get more adventurous, but that funk riffs were the most testing to play and to stay in time. I just kept playing the same riff over and over for 5 minutes, just trying to feel the beat in the song and absorb it. I knew I was on the way when I stopped frowning, started grinning and bopping to the groove. Since I play with headphones, my wife thought this was very funny.
Good luck!