Well, Horstl is right, its all milli-seconds difference per line, but the way I look at it, it all adds up. One milli-second faster here and there, always writing code to make mIRC work the least as possible all adds up.

Guidelines?

Always try to use proper mIRC coding.

if (comparison) { command }

yes I don't have to use { } around command but that means mIRC takes the time to put them there.

Use static names and paths when possible.
Something like $dname will return the dialog name in the event, but writing the actual dialog name instead is faster, making mIRC work less. Do this whenever possible.

Hash Tables are great and fast. I also like to keep my variable list as clean as possible.

$+(data1,data2) is faster than data1 $+ data2

If you do one or two of these things once in your code you may not notice much of a difference. But if you adopt this in all your code I guarantee you will see a difference in speed and response.