It's in the name "Web Log", "Weblog", "Blog". See? Notice all of those successful blogs out there? The ones you read every day? Notice the stuff that you find on them? You find things that you are seeking. You search for what you are looking for, and there is someone talking about it.
That is what your blog is. A log. Some log every day life. Ups and downs. Some update the news on a given subject. Some share information on a specific topic curated from within a larger, more broad set of topics.
That's the generalized rule, and this is another generalized rule: Large blogs [staffed blogs] focus broadly, and typically smaller blogs tend to stay targeted to a very specific point. One person typically will write about one aspect of a broad whole, the broad wholes they find being written about on those larger sites.
A small gaming site would cover one genre of video games, logging the news from a number of larger sites, making it easier for other users to navigate to their particular interest at that moment, rather than having to sort through a larger wide-audience site like IGN or Game Informer when all they want to know about is MMORPG or GTA V at that moment.
By the way: That is what Google looks for - web surfing experiences made easier. A lot of people are worried about Google updates, but if I understand correctly what has happened over the last year, the gates have actually opened up in new ways and it will be easier than ever for a whole lot of new faces to do well online - by applying themselves, and logging their own experiences from their own interests, in multiple blogs.
Gone are the days that titling, meta tagging, and frequency of search terms riddled in your posts can get you a really successful site that doesn't really have any value in it. And likewise, gone are the days that you actually put sincere work into something and have it never ranks because of those exploits. The way I see it, the only people who can really be upset, are the people who deprived everyone of quality search results just because they wanted to be #1 for "buy a new lawnmower". That's a good thing.
Anyway, sorry for my diversion: Regardless the type, size, or topic of a blog, they are all still doing the same thing - Sharing information through experience. A sports blogger might cover the entire NFL, NBA, MLB, and NHL line. Or, he or she may pick only one team, from one genre of sport, or even just one player - that blogger who adores sports is going to be seeking out information for himself and sharing it with others at whichever level the blog resides in a topic.
The only time you can possibly "struggle with finding a niche" is when your strict foremost goal is to make money with your website as a business. That is when it gets tricky. At that point, you are not writing a blog. You are marketing, selling, servicing, and most importantly competing. And if that's what you're doing, then you can go ahead and add a blog to your site, and log the experiences, changes, news, and offers that are had at your site or through your business. But you'll still need to treat it as exactly that; A blog.
You take what you're already doing, what you're already experiencing, and condense it for others who will be looking for that information as well. Evergreen, timely, it doesn't matter. Sports, clothing designers - doesn't matter. I do a lot of reading about affiliate marketing, making money online, blogging, and WordPress. So, I started this site about that. I share things I have learned, and as times goes on, I will have a large body of content for people to find when they visit my site based on those topics.
I do my case studies on sites that pay their visitors right now, and hope to find plenty of places to conduct those (hint: Put your links for me to join in your comment), but you can expect this blog to share information about plugins for WordPress, running websites, and my experiences in the marketing world online alongside those case studies.
I will share things I am reading, I'll link to places I found those things, I'll keep a log of my own experiences. The whole site, is one big case study. And that is what I am putting on this post: Blogs are All case studies, and as long as it is written with quality and as long as the topic of a blog comes from one that has many different aspects, it can be successful as a hub for one or more of those aspects. Targeting a specific group of the whole, rather than the whole.
You've got to let people know your blog exists of course, but that's the general rule: Fill a gap, or fill it better. Sub-niche a genre or medium, or supplement information. Do it with quality and somewhat frequently. The people you do show your site to, provided it's relevant to them or solves a problem for them, will visit your site.
It's a log. Treat it like one, use it as one, and log what you're into or what you want people to know or be able to easily find thanks to you. You can be educational like this post, you can share news or links/showcases/shares other times, you can focus on one athlete or the whole league - share it with integrity, update often, and you will see results as a blogger. Treat your blog as exactly that; A blog.