Are you doing the great south? Did that last year, won't be doing it this year tho...cripple.
Start slowly is my advice, and when it hurts like f*ck and you think you need to stop, think of something that inspires you, such as MLT, or soldiers dying for there countries or summit random! Seems weird but really helped me get past certain barriers previously.
I'll prob do the new forest half and GSR next year, hopefully following it up with the FLM year after, depending on how the knee recovers....