1. If you pick the right personnel, there will always be a time when you can play each player. Think about when these times are for each player on your team and allow them to excel in these situations.
2. Be clear to your teammates about the team's sub-calling philosophy. If it changes for a tournament, don't make it a hush hush operation—let everyone know so nothing is a surprise.
3. When at all possible, have someone who's not playing (a coach or designated sub-caller, perhaps even an injured player) call subs. Sub-calling and playing time create the most opportunities for team chemistry to breakdown and when your playing time, which directly relates to most people's enjoyment of their playing, is dictated by peers, it can get ugly, fast.
4. Sub to win. At the elite level, everyone would rather be on a winning team and play one point per game than be on a losing team and play five points per game. Or at least we should—if people aren't on board with this—reconsider their options, which is fine.
5. Don't get caught up in specialization. I think this may apply even more to Women's Ultimate than Open Ultimate, but if you have a good player on your team, don't keep her in the "D line" or "O line" or "Zone" or whatever you think she is best at if she might be able to help the team in lots of different situations. The reality is that there will always be turnovers, teams will always throw different D and O looks, so just play your strong players that get the job done in all situations and be creative with their supporting cast.