Mostly it is a matter of spreading the word and enthusing with friends.
Writing to your MP or going to see him or her are good moves. Ask them to take matters up with the relevant minister.
Beyond that if you still have to energy is to collect a petition on the specific issue of concern and presenting it to the MP.
If more is needed get a group together and go to see the MP together or hold a public meeting.
Anything else needs to abide by the law and not be rude or hurt anybody or any property.
But it is OK in a democracy to try by fair and legal means to persuade elected representatives to do the right thing.