Getting dips appear in uniform pattern
I seem to get dips appear in uniform pattern, Is this trowel technique? Happens more when plaster is firming up a lot and is hard to apply. Can be felt in finish and seen through paint.
When applying the 2nd coat of plaster ensure your trowel acts in a flattening way rather than scraping.
How to flatten and not just scrape a few high spots
It is all to do with firm pressure and the angle of your trowel. It is very hard to give specific advice, as trowels vary, but as an approximate guide the leading edge of trowel will be between 10mm and 20mm off the wall.
Then with firm pressure any excess plaster will be scraped off the highs and be forced into the low spots. This will give you a flat surface. It is also important in the nest stage (stage 4) to also ensure your trowel is fairly flat and firm pressure applied to push the highs into the lows. If your arm doesn't ache then you're probably not pushing hard enough. You should be able to run your trowel across the wall and if it is the correct angle no plaster will be scraped of and be collected on your trowel. It will instead be scraped off and pushed into the lows.
Then in the later stages as the plaster firms up this trowel angle will not be so crucial.