SLADE3's basically gonna be your go-to program for makin Doom mods in general, so it's important you learn how to use it.
Theres a whole slew of tutorials on how to do various things in SLADE3 like makin maps, editing texture and flat entries, and editing scripts.
you got some tutorials on the official SLADE website:
http://slade.mancubus.net/index.php?page=wiki&wikipage=Tutorials
And there's quite a few videos on Youtube explaining how to do certain things, like this one!
just be aware that a lot of these pertain to Doom and not SRB2.
As for tips. I'd say that even though SLADE3 offers a lot in the way of modding, you shouldn't make it the only programs you use. While it offers thing like map editing and texture editors. The features offered in these tools are pretty barebones and are overall limiting in what you can do, (Heck, SLADE's map editor is practically useless in regards to SRB2 as it doesn't support SRB2's FOF's and slopes.) There's other dedicated programs that can do stuff like mapping much better, such as Zone Builder.