Slim_slag and turbine say it all.
What I find works for me is the following, assume you have captured the loc & glideslope.
First set the rate of descent using the power, the PA28 I use requires about 1800-1900 to maintain a 500' descent. You should find once this is set you dont really need to adjust the yoke and the glideslope should stay pretty much spot on albiet the odd correction..
As you say its all down to SMALL corrections, force yourself not to chase the needles even if you think you should be making larger ones. With the loc if you are making a adjustment left or right try turning and counting either '1' or '1-2' before going wings level again - this basically forces you to make small corrections until you discipline yourself to do it naturally, then wait a bit and see what happens - if you dont get the required outcome then try it again. The closer you get the smaller the adjustment or you will end up getting a FSD and going missed.
Practice makes perfect on the ILS.