Tips. Two.

1. [u]Learn and use the alternate fingering of open G [/u]using 2nd, 3rd and 4th fingers. If memory recalls accurately (?), that's an alternate open G fingering Lisa teaches alongside conventional open G somewhere in F1 anyway.

Why? You'll need to be able to use that 2, 3, 4 finger formation later anyway when you, A. use barre chords, or B. encounter certain progressions in songs. i.e. "Lyin' Eyes" G, G7, C, Am, D7 ..etc. I've taught myself to do both to the point I can use either rote at will by recall association with individual progressions in songs as required.

2. [u]Tenacious Repetition[/u]. Yep. Just keep at practising forming those finger formations and changes slowly over and over until it all becomes rote. Ain't no 'secret' to it other than that. Focus on forming them accurately so each chord sounds clearly noting how your individual hand's thumb and fingers fall to achieve it. Once you have each formations forming feeling less awkward, alternate from one to the other to introduce the change focusing upon doing so smoothly and fluidly rather than fast. Same with a three chord progression e.g. G, G7, C and subsequently its riff. The speed will come until you can play them and the riff at tempo.

How do I know? "Lyin' Eyes". Really wanting to play that song and its pretty, pretty riff fueled the mojo effortlessly. Have fun.

Cheers.