Spanking ass and balls, how to self-spank properly?

[Jaro]

Newbie sub question here.

Sometimes I have to slap my ass or balls. So far I have done so using just my bare hands.

My ass doesn't hurt so much if I do that to myself.
My balls hurt tremendously with only a little slap.

How do I slap myself properly so that my ass and balls receive a proper amount of pain? Not too much, but enough to constitute a proper punishment.
And using my bare hands only.

I realize what "proper amount of pain" means is highly subjective and depends greatly on a subs pain tolerance level and the amount of punishment needed.
I'm just looking for ideas here for me and I think my pain tolerance level is actually pretty low.