Sub4Sub is such a bad tactic as everyone has already mentioned - though I think a c2a of "remember to like comment & subscriber" could maybe useful in some circumstances, though it's very youtuber-ey and I don't think its appropriate here on tapas since, at least early on, a good portion of your readers will be other creators - maybe on webtoons it's more okay. I think in general you should be using your ad-space to promote other things, such as your support networks (Ko-fi/Patreon/tips/stuff you sell) and other content that you make (such as your twitter & instagram)
for myself - I've got this banner that I put at the end of my pages:
It's less about "begging" than it is showing readers who are interested in supporting me the different options they can take, and more importantly what they can get in return. Tippers can AMA - you can see my illustrations if you check out my ko-fi, and patron's get early access/behind the scenes, and I've neglected to mention it in the banner, exclusive zines (I use a different banner to promote those)
Also - yes I know there are typo's and miss-spelled words in it. The other half of this tactic is about manufacturing an online persona that people can recognize as me. The color palette matches my icon that I use online - and it's written in my kinda janky goofy tone of voice.
I guess TLDR my strategy for my banner is to use it more as a branding device than as an advertisement.
(to back all of this up my BA is in advertising & marketing via social media basically - for whatever that's worth.)