Stop selling out to corporations/special interests. Stop running consultant-driven campaigns which are overly scripted, overly calculated, and uninspiring.
While this may not produce significant results immediately, it could set the stage for them to start gaining ground at some point in the not-so-distant future. Remember that Richard Ojeda ran an economically populist campaign and managed to outperform his district's partisan lean by double digits. Even though he fell short, I think it does provide a guide for Democrats to eventually regain power here in the future.
Yeah none of this will help Dems win in WV.