Interconnects
Speaker cables
power cords
I've had the most success with a top down approach. Source interconnects first, preamp to power amp interconnects second, speaker cable third, and power cords last. This is not a hard set rule by any means though. A number of variables can potentially change this order of priorities. For example, if your power is very poor, then power cords may move higher on the list, etc. If you can, get a dedicated line for your stereo. That's a fantastic improvement that's not too costly.
Speaker cables
power cords
I've had the most success with a top down approach. Source interconnects first, preamp to power amp interconnects second, speaker cable third, and power cords last. This is not a hard set rule by any means though. A number of variables can potentially change this order of priorities. For example, if your power is very poor, then power cords may move higher on the list, etc. If you can, get a dedicated line for your stereo. That's a fantastic improvement that's not too costly.