I am a self-coached athlete for several reasons. The most obvious is that I'm a beginner, an amatuer, and have little to no talent for the sport. For another reason, check my occupation. However, I still take planning my training and racing very seriously. Last year I used two books: Total Heartrate Training and The Triathlete's Training Bible both by Joe Friel.
This fall I used a training plan from Runner's World Smart Coach to train for my half-marathon. I liked the way that running plan was structured, so I am using a similar one for my base period running training. I combined that plan with what I used last year to come up with a plan for this year. The Runner's World plan had me doing a longish tempo run mid-week which does not work for me when darkness comes right when I get home from work. I kept the Sunday long run, but spread the weekly miles out more evenly. I don't plan on doing another half marathon until the fall, so the longish run seemed unnecessary. Also, all my triathlons this year will be sprint distance, so the tempo run was traded for shorter intervals.
Who knows how this will all work out. Personally, I think that at my level, just getting out there and running, biking, and swimming will show improvement. I'm just ready to tri it again this season!