-It is better to do not do that. (No)
-It is better to not do that. (okay)
-It was better to not do that (okay)
-It is better, if I do "not" do that (Okay, as long as you use "not" instead of "no")
-It was better, if I did not do that (No)
-It became better, if I did not do that. (No)
-It is better (that) the work is not done (you can probably say this, but I’m not sure what you trying to convey.)
-It was better (that) the work was not done (same comment as above)
-The undone work is better (No, this does not make sense)