I am completely and utterly confused about team gameplanning.  

Tempo:  Tempo just confounds me.  What are the factors that go into choosing what tempo you will play against your opponent?  Your team's stamina vs. your opponent?  Overall talent of your team vs theirs?  Team Depth?  Speed?  Which offense defense you play?  What offense defense they play?  What is it that makes you play slowdown vs. normal vs. uptempo?

Defensive positioning:  I play 2-3 zone and have a very good rebounding team.  I don't have great defensive ratings, but I have some great shotblockers.  The defense on the perimeter isn't great, but it's not terrible either.  Should I go +'s to help my perimeter defenders?  Would going +'s still allow opposing teams to knock in 3s but also crash the boards better making it pointless?  Should I go -'s to get even more rebounds and risk having teams just rain 3s?

Again, I am at a loss here.  Any help is greatly appreciated.

For tempo, I look at my Ath. and Spd. ratings vs. my opponent -- If both are higher, I go uptempo unless I'm playing a fullcourt press defense (there's a phrase in one of the guides that the press troubles uptempo teams...took that to mean don't do it, so never have)...if both are lower, I run slowdown. If I'm playing a Sim team with 3+ walkons, I'll run uptempo unless there's a clear reason not to.

Positioning is a bit trickier...early in the year I start by looking at my rebounding rating vs. the opponent and then bump the +/- based on the opp's LP vs. PER differential. If the PER rating is particularly sub-average, I'll collapse regardless...I want a team that's probably not going to hit better than 25-30 percent to shoot all night long. I'll just collapse and grab the rebounds and trigger my offense. As things drift later in the season, I'll start looking more at a team's actual stats rather than the ratings to make those sorts of determinations. In conf. games, I base a lot of my adjustments on what happened the first game vs. the opponent with the ratings and season stat trends a secondary influence.

Thanks rednu, that was very helpful.

Tempo:  I go uptempo if: 

1)  I am deeper than my opponent,
2) my bench is better than his bench and my starters are worse. 
3) My team is overall favored
4)  I have more stamina in general
5)  He has less than 10 healthy players
6)  I want a game with more fouls and more FTA, i.e. he shoots FTs poorly or I shoot them well
7)  More likely to go uptempo at home.

Factors I look at for positioning:
My teams Def/Ath/Spd matchups (I play man) to his
His % of shots from 3point land
Rebounding Margin
What I think he will do
How good are the 2 teams 
Home/Away

Start with your team first. If you lack stamina and/or depth it's hard to run up tempo against anyone. A lot of teams will run slowdown when facing a clearly superior team, hoping to reduce the number of scoring chances for the opponent and keeping the game close. Use the exhibition games and non con schedule to play with the positioning settings. With "my" past teams, the plus settings seldom seem to affect outside shooting and definitely reduce rebounding, while minus settings increase rebounding but also increase fouls. Warning: Mileage may vary.