Try to hold the miniature with the most touchpoints possible (like here 3 fingers = 3 touchpoints). Alternative is to glue them (I use Pritt poster buddies) on an empty medicine bottle or cork !
Try to rest your forearm and holding hand on the table in order to limit your movement. Rest your arm holding the brush also on the table, if needed, even your painting hand holding the brush on the table so that only your fingers are doing the brush movements.
It’s hard to paint details when your paint is “thick” so always water down your paint so that it’s easier to apply on your details. You can make a wet palette (see tutorial from Guslado’s Games) or buy one like I did; the Privateer Press P3 Wet Palette Model Kit (it has refill kits) that works great. Here’s how to work with it efficiently.