Sparklefizz
I would never vote tactically. It’s not the Eurovision Song Contest
How else, under the first past the post system, can you try and get the result you want - or, more to the point, prevent the result you definitely do not want? If people blindly vote for "their" party, this will often lead to the one result they do not want.
For instance, if you are a Labour supporter and the local Labour candidate cannot possibly win (judging by past voting habits), then voting for them is effectively a vote for the Tories. If there were say a Lib Dem candidate who stood a chance of ousting the Tory, might it not be better to vote for them? As a Labour supporter, the last thing one wants is to give the Tories more seats.