bankroll management

Your bankroll is the money you have set aside for playing poker. If playing online, it is the amount of your initial deposit plus any wins or losses on that account. A common mistake by beginners into online poker is playing at a table stake that is too high for their bankroll. This will have the adverse effect of going broke in short order. Not a pleasant experience. Correct bankroll management will ensure maximum efficiency by selecting the appropriate stake level to play at, and dropping down in stakes when the balance in the account reaches the limit for that level.
As a general rule of thumb is 40 buy ins at the level you wish to play. So if you are playing $5 sit and go games, you want to work with $200. If you are working with $50-100 deposit, you want to play low limit micro games until you build up your bankroll to $200 before moving up on stakes.

In the book "Secrets of Sit and Gos" by Phill Shaw, Bankroll management is covered in the context of building a $200 deposit into $100,000 in a year playing 5000 sit and Go No Limit Texas Hold'em. At the $100 or less buy in games, the author suggests an expected ROI (return on investment) of at least 15% which corresponds to a minimum bankroll of 40 buy ins. At the midrange $100 - 400 a ROI of 10% and higher levels of $500+ ROI of 5% can be achieved. With about 14 games a day if multi tabling 4 tables could be done in 2-3 hours a day.

The climb from $5 buy in up to $1000 looks like this.. (buy in - bankroll)
$5    $200
$10  $400
$20  $800
$30  $1200
$50  $2000

$100  $6000
$200  $12000
$300  $18000
$500  $50000
$1000  $100000

There you have it. $200 to $100,000 in a year. Start out with $100 deposit, build it up to 200-400-800 moving up in stakes as you go.