I'm not a member of any party, but my inclination is towards the Greens.
Your view that the GPEW has not been strong enough may be flawed, but only in some respects.
Local elections are atypical - younger voters are disengaged from local politics, and local issues can sway some local elections enormously.
However, there are probably a lot of lessons to come out of this week.
Some of them may include
•Less reliance on the perceived charisma of a single leader
•Getting younger people out to vote
•Being more savvy about the media and how it attacks
•Funding - it's always about the money sadly.
My further hope for the General Election is for strategic alliances to prevent 'vote splitting' in certain areas. This would mean swallowing a lot of pride, and quashing many egos.
In this I would include Labour, Lib Dems and perhaps the National parties (who I know very little about).
Other than that - I dunno!