Most useful tweaks that are sensible and really make a noticeable improvement

So after reading the thread of useless tweaks I'd  be interested the communities opinions of useful tweaks. I may be rehashing a previous thread but times change as do useful tweaks.

I have found that in my case the following were useful, immediate and audible,
In order of priority in my opinion
1 Room treatment
2 Speaker location, ie proper setup
3 Subwoofer location (if used)
4 Subwoofer integration
5 Component isolation
6 Cables, all SC/IC etc, normally I would not mention cables but did have an ear opening epiphany that makes me believe cables are system dependant and I do not mean directionality.

So if anybody has anything to add, please do so as none of us are ever too old to learn.