It's my third Lora today and clearly I still don't know what I'm doing cause this one is not so great >_< I'll probably make v2 but you can still get somewhat good results as in my examples so I hope it will still be useful.
I wanted it to work using phrases sakata gintoki, gintoki kimono and shiroyasha. But in the end it's pretty lackluster. Use sakata gintoki, gintoki kimono, open clothes for regular Gintoki outfit. Should probably work even better if you'll put shiroyasha, haori in negative prompt.
I'm not able to get shiroyasha outfit consistently right now, but maybe you'll be more lucky. Still, for regular Gintoki it's not bad. Using some bloody words like blood on clothes will probably get shiroyasha more often. So in the end danbooru tags are your friend.
Use Lora weight 0.5-0.6. Also hires-fix helps a lot, eyes often looks weird for me on lowres results.