There are several different tunings people use for slide- open e is pretty cool. My makeshift system for slide guitar tuning improvisation may be fun: Start out in a drop D (Drop your bass E down to a D)

Play alternating bass between this D and the next D down

Then just start sliding away while tuning the rest to anywhere they sound good

It works well. (When you make up a good tuning, figure out what it is and write it down!)

-P)(