This mod adds a neat visual aid to placing stairs and slabs, and some extra items as well. When you are holding a supported object and pointing at a location you can place said object a visual will appear showing the rotation the node will be placed in. You can get alternate rotations by holding the sneak key.

Download Luanti: https://www.luanti.org/downloads/

https://www.nathansalapat.com/luanti/placement-preview