Don't go pumping 50w unless for example you've got a quad coil setup under 0.15ohms.
Huh? Ive run many builds that were way over .15 over 50 watts just fine and none were dual coils. Advise like this really dosent help to much. It just makes a beginning vaper think he may be doing something wrong when he keeps his simple dual 9 wrap 24G coil under 30 watts and isnt getting a good vape.
The only thing that is a definite in coil building is Ohms Law. screw that up and your mod can become a bomb. Past that it is mostly subjective.
When I build coils after they are wrapped and installed and I have gotten the hot spots out I fire them and see if they come up to temp (Nice bright red, but not white hot) quickly. I normally take a 3-6 second puff, so i make sure my coil will come to temp with in that amount of time. If there is to much metal there I have to increase the power.
Overall there is no set run X coil at Y power. it comes down to what works for you, gives a good vape with no dry hits. Wicking and airflow have a big play in this too. massive air can help cool an otherwise too warm coil, where the opposit, a perfect coil with to little air can be to hot and singe the wicking.