how do you fix displacement artifacts? Like black lines and so on.

A pretty well documented subject, im sure you will be able to find alot of threads on the topic. Sounds like a Displacement Bound issue, but i have no idea, no screenshot, no file.

Well can someone tell me the common practice when creating one?

Try the Houdini Documentation.

Nothing there I can find, but i figured out by going to my geo and turning on precompute bounds, is there a way I can implement this into the displacement shader itself?

There is actually lots of content there regarding displacement bounds, not to mention the forums. Using search can help find these topics.

This is one of many pages that help set it up.

http://www.sidefx.com/docs/houdini12.1/howto/sopocean [sidefx.com]

But again, this is no file nor screenshot to be able to identify the problem. This might not even be the solution to your problem.

http://www.sidefx.com/docs/houdini12.1/rendering/understanding#id230468 [sidefx.com]
http://www.sidefx.com/docs/houdini12.1/props/mantra#id219454 [sidefx.com]

And as always have a look at the default shaders like the Mantra Surface Material as they have this hooked up already.

I fixed it. Does this show you how to add this to the shader it self (Displacement bounds).

yes