A strategy is a sort of tool that helps you to visualise the problem better and hence help you to work it out. If you had to undo a few screws to remove a panel to get to the inside of something you suspected of not working properly, you wouldn't look for a hammer or saw or knife to remove the panel, you would look for a suitable screwdriver, wouldn't you? In the same way, the strategy you use to solve a problem in mathematics would need to suit the problem. So a strategy is a method to help you solve the problem.
I've used all sorts of strategies, including looking at the problem from a different angle, drawing a picture or graph, solving a simpler but similar problem, making a rough guess or estimate, using logical reasoning, etc. Take Q3, for example, I would do as I suggested in my answer and count how many triangles of a particular shape there are. Do this for all the shapes there are and then add up the counts. This avoids losing count, or counting something twice, or missing something out, and it's easier to check one of the counts instead of starting all over again from scratch. You could say this method is compiling an organised list.
So it's entirely up to you. You can even make models. In Q7 you could use actual marbles or some other object to represent a marble. Actually handling something material can help a lot in converting the abstract mathematics into something practical.
For Q4 you could draw a picture or graph showing the diminishing height of each bounce.
You don't always need a strategy because you're able to solve the problem directly.
When you look at my answers, make sure you understand them, and then you will be able to explain in your own words how YOU arrived at the answers. I've indicated to a certain extent how you might do this. But you need to make absolutely sure you understand the answers.