Well, though I haven't actually made up my mind which way I'm personally thinking of voting (save for a few definite ideas of who I won't), I definitely know I won't get the opportunity to do so for Starmer, Sunak
or Farage, because none of them are going to be on my voting-slip. (Between them, slightly under 235,000 people could do, but only one of them. Realistically, there's an upper-limit of 100k votes likely to go between them, and possibly as low as 50k (with similar number of votes against them). Same sort of thing goes for Davey, et al.
Whereas Foster, Swinney, etc are even more unvotable-for (or against) on this occasion.
Apart from actual trying to be clever about everything, though, perhaps one should vote for the actual candidates that best represent one's views. If they get to represent your constituency (and, persumably, a party/leadership that also
roughly sits well with you), there's a better chance that their party (and ideas of the leader, if not the
choice of one) swings that bit closer to your shared values in response. Even if they lose, it sends a message to the others (same party and others, with any luck) that there's an interest in
more of their take on things.
Not that party-wide manifestos should be ignored, of course. I must say I am thoroughly reading them, as well. In particular, I do quite like the following promise from a party that's unfortunately not standing in my area...:
Greener Cars
Once in Government we promise to have more green cars on our roads. Politicians will have fluorescent green cars so that everyone can see them coming.