Spark is a very different engine from others
Thus, Spark is only set for Natural Selection 2
Here are some beginner's advice :
Read everything[]
Read as much documentation and watch as many videos as you can. Don't worry, there isn't that much since it's not a very known engine.
Make a greybox map[]
Greybox is the best way to begin a map. Use a 256 units scale for everything, this can be quick
Remember you can download an example map here : https://forums.unknownworlds.com/discussion/155728/ns2-veil-layout-example-map
Beware making duplicate points/lines.[]
Example : you should not make an extrude room attached to one another. Or you will have to use select 2 points and then "Weld Selected vertices" (+snap to min grid).
Best way to know if something is in double is to select it then delete it (then CTRL + Z)
Make simple geometry[]
Only use 45° angles
Make complex geometry not welded to your main greybox map.
Use stuff from existing maps[]
It's sometimes more simple to open an existing official map (remember you can open any *.level files) and take prefabs and copy/paste props from an existing map rather than searching with the prop explorer.
Although it can be considered as "cheating", I can guarantee that it's the best way to go fast and finding interesting and accurate props for the room you are designing.
Spark Editor - Maps • Spark Editor • Spark Game Entity • Spark Entity List • Spark Decals • Spark Custom Materials • Spark Custom Skybox • Spark Lights • Spark Sounds • Valve Hammer to Spark • Spark Troubleshooting • Spark Beginner Tricks • Spark Editor Final Checklist
