How do you install my car stereo to have constant power for memory?

How do you install my car stereo to have constant power for memory?
depending on the stereo,most I have installed will have a power wire,some times yellow orange or red,and there will be a blue for power antenna,one of the power wires will connect to the ignition side of the fuse box,(this will only have 12 volts when the key switch is on)and the memory wire will connect to a constant power supply,like the battery or the fuse box that where there is 12 volts with the key on or off,make sure there are the correct size fuses inline for each positive wire