Small paint job...

I have a replacement front wing to fit - with a few small bits of rusty paintwork to fix first. The tricky bit is an obvious patch about as big as a 20c piece.
Am planning to start by scraping off all the loose paint, then painting the bare/rusty metal with hammerite anti-rust paint, then cover it with a few layers of my MX5 paint (touch-up tin or spray). The thing is, I don't know how to make the paint smooth & join it nicely to the existing paint.
Can any of you wise people make some suggestions? All gratefully received.
Am planning to start by scraping off all the loose paint, then painting the bare/rusty metal with hammerite anti-rust paint, then cover it with a few layers of my MX5 paint (touch-up tin or spray). The thing is, I don't know how to make the paint smooth & join it nicely to the existing paint.
Can any of you wise people make some suggestions? All gratefully received.