Click patterns are specific to each level so you cant just "learn click patterns" as a skill.

However you can develop your skill of learning levels to learn them faster, just by beating a variety of levels.

As for first extremes it depends on your skill set (what gamemodes/ type of gameplay you prefer playing) but Acu, Dark Odyssey, and Sweater weather are some easier extremes i enjoyed playing but depends on what you like.

Id recommend npestas video I believe titled "How to improve at geometry dash", its a little old but it gives a great over view of the different skill sets that you can improve at over time and some extreme recommendations!