Question :  What is the best system for deciding which plays to run when in solo mode?

Answer :  Here is what we have in the rules.

Roll the dice to decide what play # to use and proceed from there. For a more accurate offensive selection, separate the (3) passing plays from the (3) rushing plays. To pick if it will be a run/pass roll the 24 sided dice. Check your team sheet (see below) and look at the # of runs. If your roll is <= to that # (11 in the example) then it will be a run. Anything higher will be a pass. Once you determine if it is a pass/run then randomly pick from your run or pass cards as appropriate.

From there, you roll which play result as usual.

If you roll a 21 and only have 14 plays then go to the top of that run play list and use the first unused. If all of those plays are used then go to another run type (I usually go to the run that has the most available). If you use all your plays then you can start over running any of them again.