You shouldn't have to tell them anything! If you are producing quality content that they like and engaging/making friends with them on their own posts, they will follow you. :)
For example, in real life you wouldn't go up to some stranger whom you overheard say something that you agree with and say: "HEY IF YOU'LL BE MY FRIEND, I'LL BE YOURS!!!!1!1!!1", right? If someone did that to me, I'd be like, "Uh, you're a creep, go away". haha
Btw, your engagement on my post, has gained you a new follower. Now show me what kind of awesome content you can create!
wow!!! really?! in that case a lot of thanks and i upvoted now this blog.. anyway i'll be keeping in touch with your blogs...
Haha Ok, thanks! Have an awesome day, man!