I'm waiting on a render, and I've acquired a small following here over the last few days, so, why not a very short thread about how to "get gud" with Houdini in an organized way...

Start with SOPS. Live in it. Do everything in it. Master it. This is the meat and potatoes of Houdini, and you would be surprised at all the amazing things you can do without simulations.

Now render something. Mantra too intimidating? Go with Redshift or Octane. Both are really easy to use and incredibly fast, if you have the hardware. In any case, take your basic (or not so basic) SOPS stuff and learn how to make it look amazing through light and color.

Now you are ready for simulations. But, don't reach for that pyro stuff just yet. Start with POPS. Learn about DOP network flow, simple pop stuff, and gradually build in complexity until you have it down and really understand it.

Next logical step from POPS is Flip Fluids. POPS (forces and methodologies) goes with FLIP like ice cream goes with hot apple pie.

You have POPS down? Now, pick one of two: vellum (cloth and grains, etc.) or rigid bodies. You can use knowledge from POPS in both of these effects.

Finally, smoke and pyro. This is by far the hardest, and has the most parameters (and time-intensive simulations), so I leave it for last.

As a bonus, learn CHOPS and rigging!

And... render finished. Back to work!

I didn't include VOPS/Vex in here, but I should have. VOPS, after you feel comfortable with basic SOPS stuff. VOPS may seem like another world, but it's all the same as everything else in Houdini. Just nodes manipulating data. Vex is something to circle back to much later.

For tutorial/written word learning, here are great resources:

https://www.sidefx.com/learn/ 
https://www.tokeru.com/cgwiki/?title=Houdini
https://www.toadstorm.com/blog/ 

And all things Knipping: http://www.appliedhoudini.com/