I’ll second what’s been said above. There’s no super quick way to increase your SEO. It’s a marathon, not a sprint.
I’ll always suggest looking at your content first of all. If you’re not providing good content that your ideal buying would like to consume then you’re shooting yourself in the foot.
Definitely, check out Google’s PageSpeed tool. Don’t take it as a bible or anything but on images especially not having them optimised is a quick way to annoy customers with slow load times.