How do I prep and paint a table set?

Not sure what reddit I should be posting this to, but I’ve got an metal outdoor table set that I want to paint, I tried painting it a while ago all the paint bubbled up and started chipping off, since then I have started sanding it down to get the primer and paint off and start from scratch, would anyone be able to tell me how to do it properly so I don’t mess up again, thank you :)