If you are looking to play poker just to have a bit of fun, then don't invest any more than what would be considered 'fun' to lose. Hence, if $50 is acceptable to lose then only invest $50 and see if you can win with that amount.

If you are a seasoned player who has proven to be a winner then you should be able to bank 200 big bets at the limit you play. Hence, if you play $5-$10, you should have a $2000 bankroll ($10 * 200). Having this amount as your bankroll if you play at $5/$10 for example will prevent you from blowing your entire poker bankroll because of one bad run.

Some say that 200 big bets is too few, but I believe that you need to be reasonable about potential losses until you are sure that you will not lose your entire bankroll. You don't really want to invest more than 200 big bets unless you've proven that you're successful at that limit.

A few tips to keep in mind for bankroll management

Never play in a game that is beyond your bankroll, even if you are doing well try to stick to the limits you are successful with until you have the recommended bankroll to move up a limit.

Never buy into a cash game or a Sit & Go with all of your bankroll. Try to spread your bankroll to as many tables as you can in order to give your self the best chance incase a table you sit at is cold. You should not sit at a table with more than 10% of your bankroll, which I think is too little, but this will ensure you are never at risk of finishing your bankroll.

You should consider leaving a table once you have doubled up and move to a new table in order to keep adding to your bankroll and not risk losing your current stack.

If you do realize that a table you have sat at is cold i.e. you are not getting cards or when you do you are not winning then leave that table as soon as possible. If you are playing a tight, decent game and have lost more than 25% of your initial starting chip stack, then you should seriously consider leaving the table.

I think a lot of players would do well when applying these guidelines. One great benefit from this approach to bankroll management is that it ensures you'll be playing in games you can afford. You'll never play for very long in a game that's over your head because, when you're losing, you'll have no choice but to drop down to a smaller game. You can continue to sharpen your game at that lower limit until your bankroll allows you to move up and take another shot. These rules also prevent you from being completely decimated by a bad run of cards.

Dropping down and playing lower limits is difficult for a lot of players. They view it as a failure and their egos get in the way, but in order to get to the top limits you really need to slowly build your bankroll and be as responsible with your bankroll as possible. Many want to remain at the level they'd been playing and win back their losses. But this can lead to some pretty severe beats and a quick end to your bankroll.

High stakes tables are not going anywhere. so make sure that when you do sit down at a poker table, you are comfortable with the stakes, you are not playing with your rent money and you are confident that your skill level will bring the money home.