What are SeeDs?
Basically, cadets receive regular schooling as well as military training in either one of the three gardens: Balamb Garden, Galbadia Garden or Trabia Garden.
After graduation, they may then enlist in a military force. At Balamb Garden, both students and graduates can enroll in the SeeD- program and become trained mercenaries. As the story develops, it becomes clear that SeeDs are actually being trained in order to fight the impending evil: witches, and eventually the evil sorceress Ultimecia.
There are several aspects which determine your SeeD rank in FF8. First of all, you will be judged by Attack, Judgement, Conduct, Spirit and Attitude. These are being calculated as followed:
Conduct and Judgement
Both during the Dollet field exam and your Fire cavern SeeD exam, you will be confronted with timers. The Conduct and Judgement scores are based on how much time you will have left on the timer by the end of the exam. For Conduct, you will receive a higher score the more time you have left; in the Fire Cavern though you will receive a better score the closer the timer will be to zero at the end. So choose a low time limit, but don't overjudge yourself!
Attack and Spirit
These are also both determined during the Dollet field exam. Attack counts all the enemies you defeat during the exam, not counting those defeated by GFs, and only counting X-ATM092 once (receiving a 100 bonus if you manage to kill him off on the bridge!!). The spirit score will be calculated depending on how often you avoid the fight with X-ATM092, for example by hiding in the cafe or walking down the slope instead of running, thus avoiding an encounter.
Your behaviour during the Dollet exam will determine your attitude. The more shortcuts and hints you use, the less points you will receive. This includes talking to people in Balamb (losing two points if you talk to Biggs), using Selphie's shortcut from the tower on your way down, escaping from X-ATM092 in the cafe (20 points loss), failing to save the dog (10 points loss) and one point loss every time you try to leave to the tower before Seifer tells you to do so.
SeeD tests and ranking
Your SeeD rank provides you your main money. While you can do a lot of money by haggling and selling, you won't have to if you start off with a high SeeD- rank. In fact, even if you buy a lot of things you mgiht just end up with over a million Gil and ask yourself where on earth all that money came from even though you didn't do anything. Your money will automatically be transferred to you every once in a while. The higher your SeeD- rank is, the more money you will get. It's that easy.
So, how to raise your rank, you ask? Simple. Once you passed your SeeD- exam with flying colours, you will be able to select the Tutorial- option in your menu screen (press "D" on the keyboard/ Circle on the control pad). Select SeeD- test, and each time you complete a test you will go up one level! Not only that, but getting all the questions right might tell you a few interesting things about junctioning you might not have known before. Anyway, my suggestion: As soon as you passed the Fire Cavern exam, use this table, do all the tests up to level 30 and never worry about your money again.
How to get to level A, raise your level without doing the tests and most importantly, not lose your ranks you ask? Well, this might be a bit harder. Several aspects play into this, one major one being your behaviour on the field and in battle. If you have the tendency to run from battles a lot, you will notice that your rank will drop. If you never run and fight a lot of enemies, your level will stay the way it is or you will even gain a rank! Furthermore, you should be nice to people and generally perform well in the minigames and missions (such as saving Rinoa quickly on Disc 3, or performing well during the Forest Owl's mission). It doesn't always affect your SeeD rank, but you never know. Besides, you'll look better.