Power is calculated as I^2.R or V^2/R If you know the current through them or the voltage across them, then knowing the resistance, calculating the power is easy.
For example the resistor between the output and the adj pin might be 120 ohms. It will have 1.25 volts across it, the power dissipates is 1.25*1.25/120 = 0.01 watts. This is way below 0.25W.
Let's assume your output voltage is 12V. So the voltage across the lower resistor will be 10.75V (and it's value will be about 1k) the power dissipated is about 0.12W -- and this is almost exactly half of 0.25W, so I probably would use a 0.25W resistor and not worry about it.
1% resistors will not necessarily give you a more precises output voltage. But it certainly won't be worse! The main variable is the LM317 which has only about 5% accuracy, so it will swamp the resistors in terms of error.