i have been suffering from this since being stupid enough to solo at SITS last year. Lots of rest has helped, but it still niggles. Reading the Andy Pruitt bike medicine book, it would seem that dropping the saddle height a little can help (seems to have helped me) and also look at the angle of your cleats if you run clipless. He says that too much toe pointing ‘in’ can aggravate it too – putting pressure on the outside of the knee.
It is also suggested that a decent ‘base’ mileage of training is helpful to reduce this, so build uo very gradually. Although oddly, I have been finding that riding SS off road is not too bad (probably due to standing a lot) whereas even a fairly short gentle road ride aggravates it a lot.