Since these are clearly not true, we can speculate on the conditions under which gases will behave most ideally as well as the types of gas particles which will tend to deviate most from ideal behavior.

At higher pressures gas molecules are crowded closer together. Thus the volume occupied by the actual molecules is a larger fraction of the volume occupied by the gas as a whole.

At higher pressures, intermolecular attractions also become more significant since the molecules are at close range. For this reason most gases condense to liquids under sufficient pressure. The ideal gas law does not predict this.

A similar effect of the real intermolecular forces is seen at lower temperatures when gas molecules move more slowly. The decrease in kinetic energy allows for more interactions and, again, gases will generally condense if cooled sufficiently.