I generally leave the first week or so free. Then arrange 6/7 friendlies roughly 2 a week, leaving at 7 days free before the first league game of the season.
So far as selection goes, I pick my first XI for the first game & leave them on all game, only if drastically tired do I sub. Then I pick the second XI for the next game and do the same. alternating 1st and 2nd XI's through pre season. the last couple of games I will rotate the starting XI to include those that need the fitness. In the final pre season game I will rest my key players or if they need the match fitness I'll take them off after 50-60 minutes.