This is actually quite difficult because we don’t really have an idea when we should change spark plugs for our cars, but we have a slight idea that when it reaches 30,000 to 100,000 miles we should change our spark plugs already. Let’s read an article from Motoring About

When to change spark plugs

1. Engine has a rough idle
Your engine idles when it is a stationary and in this position the engine normally produces around 1000rpm. The sound the engine gives off is constant and smooth but if your spark plugs aren’t performing as they should, your engine will produce a rough and jittery sound while producing larger vibrations through the car. Not having this checked can lead to costly damage being done.

2. Having trouble starting your car?
Many people put their car not starting down to being out of fuel or having a flat battery. One possibility you may overlook is having bad or worn spark plugs. If your spark plugs don’t produce the spark needed to get the vehicle moving, then you’re going nowhere. It is also possible that faulty spark plugs are causing your battery to drain. If so you need to have your battery and spark plugs changed as soon as possible.

You can read here the full article When to change spark plugs

We can also watch a video DIY how to change our very own spark plugs.