Pay $50 and get out off Jail early in the game while many properties
remain unowned and undeveloped. You need to be in circulation.
When most properties are developed between Jail and the Go to Jail
space, roll the dice and hope you stay in Jail. It's better than paying
rent!
This is especially important when certain dangerous color groups are
heavily developed (Orange, for instance). By staying in Jail you avoid
the chance of landing on such a group before an opponent lands on yours. Remember, you still can collect rent while in Jail.
Building advances your ability to bankrupt your opponents. Many players build all they can afford. However, this strategy results in losses when houses must be torn down to pay rents or other penalties often.
You should build when you form the first complete color group. You should build when you can do so and still be left with enough cash to pay a "high probability" expense - namely, rents on Railroads or Utilities, Luxury Tax, and the "nasty" unexposed Community Chest or Chance cards. $150 to $200 is all the cash you need to hold onto if there are no other complete color groups against you. $300 to $400 in cash is recommended if there are one or more complete color groups developed against you.
You should build late in the game, in "all or nothing" situations if
you think you can financially cripple an opponent by doing so.
When you build, build according to these principles:
Build a color group up to at least three houses per property before you
start building on a second color group. (Note that rents rise
dramatically once a third house is added to a property.)
If you can afford an extra house, put it on the most expensive property
of the color group.
Build up to the fourth house or hotel level only if you have plenty of
cash to spare, unless the group is one of the first three on the board
(Dark Purple, Light Blue, Light Purple). Due to the low rents of these
groups, you should try to build hotels here.
Early in the game, develop a low rent color group as soon as you can in
an attempt to bankrupt opponents before "heavier" color groups are
developed against you.
When buying a second extra house for a three-property group, put it on
the middle property if the group is Light Blue or Orange. Put the house
on the first property if the group is Light Purple, Red, Yellow, or
Green.
If you have only low-rent color groups, quickly build three or four
houses per property to restrict the availability of houses to owners of
high-rent color groups.
Never move up to a hotel anywhere if the return of houses to the bank would enable an opponent to develop an expensive color group. (Example: the Yellow group has just been formed. There are only three houses in the bank, but six hotels. You own the light blues with four houses on each. Do not buy hotels. Doing so would give the player owning the Yellows an opportunity to build up to hotels on them.)