Its often tempting to use your vote in a tactical way: Voting against one party by voting for its biggest competitor. Sometimes this means you’re not following your core values. Here’s an article by the Green Party candidate for Hexham who describes another way:
http://tynedalegreenparty.org/2015/04/vote-for-what-you-believe-in-vote-green/
Transition Tynedale 
Hi
As a member of TT i will be following my core values which are the same as TT’s core values.
The Floating, Tactical vote, Here is my take on the subject. “””””The more people who vote green in the general election a greater % proportion the greens have. This has 2 effects, 1 Highlights the broken voting system, 2 Can push green policy’s forward as a threat to the other party’s therefore moving them towards a green agenda to retain long term vote and support. We can make a difference even when not in government.””””
It has been noticed in the hustings that “Green” issues were not pushed at Hexham were pushed at the Ponteland hustings by the none green partys this is proof that the potential Green vote is moving the other partys stance.