Another thing you MAY wish to consider is the battery itself. I know that's not your question, but the answers above are good for your question.
I assume you're messing with sub-ohm stuff since those are the main group of people that are worried about voltage drop on their mechs. When doing sub-ohm, the battery quality is even more important. Some batteries just sag in voltage when putting out a lot of amps. So it "looks" fine when measured with a multi-meter since there's very little amp draw.
Then there's cleaning of the battery contacts and battery so you get a good connection.
Also, check specs for safety.
A lot of this PITA stuff just goes away if you use higher ohm coils and/or maybe thinner wire (like 30 ga or even 32 ga). That's higher ohms and less of a problem. If you have good wicking you can still get a heck of a good vape.