Ok, you want to increase your enrollment.
You need 2 things to do that - Residential Buildings and enough Spirit to use them.
This guide is here to help you decide which academic buildings to build in pursuit of an increased spirit total.
Here is as much as you could really want to know about the Academic Buildings: https://spreadsheets.google.com/ccc?...uthkey=CIO4yTQ
Check the tabs for Residential, Academic, etc to find the information you want.
Please note - Even though you can build a Music Department at Level 8, the Music Department upgrade to Music School is locked until Level 9. It seems to be the only building that cannot be upgraded immediately after purchase.
Institute is currently the highest level upgrade for academic buildings.
It is possible to add students when your spirit is within 33% of your enrollment (neutral face displayed on the spirit indicator), but once you pass that threshold, your spirit indicator will return to a frown face and you can no longer do things with your residential buildings (including move them to storage).Example - If you have 100,011 students you have a

with 100,021 spirit; a :| with 75,021 spirit and a

with 75,001 spirit.
75,021 * 4/3 = 100,026 > 100,011 --> :|
75,001 * 4/3 = 100,001 < 100,011 -->

Please note that decorations can also add spirit - but they do not upgrade like academic buildings. As such, their usage is straight forward and doesn't need a guide like this. Academic buildings are superior to decorations when you need large amounts of spirit and only have a limited number of grid squares to place them on.
If you need residential building info, look here: http://forum.playdom.com/showthread.php?t=27279
Or Here: https://spreadsheets.google.com/ccc?...uthkey=CIO4yTQ
The chart in the excel file is up-to-date and also contains up-to-date information as of 2/2/11.