How broad (or specific) should a niche be?

Impossible to answer, Borce.

You have to ask yourself: why do we practice niche marketing? The general answer is because we want to capture a portion of the market where competition is weak enough to allow us acceptable entry. There are other reasons, of course; that's just the primary. One reason to target a sub-niche, for example, is to target strong buyers. We may, for instance, target the general niche of dating, where the buyers are a mixture of weak and strong; but target a market of people desperate for a partner who loves golf, and we likely find strong buyers.

But let's go back to the primary reason: weaker competition. We may find that, generally speaking, competition is weaker across the board; or it could be a case of easier market penetration possibilities in search engines, on Youtube, on social networks, and any other place where marketers are competing for the right sets of eyeballs. So, in a nutshell, then, we could be targeting a general niche across the board, or merely finding inroads on Youtube or Facebook.

So what does it all boil down to?

You have a product or service. You want to maximize your time and resources in promoting that product or service. Out of all the different niches to promote, at this point in time, is this the one that is best for you? The best allocation of time and money? The answer: it depends on how many units (or actions) you expect to sell (or generate). It could be that the market for one-eared pink fluffy bunny rabbits is wide open, no competition, but only 30 people in the world want one each month. On the other hand, pink fluffy rabbits are in high demand, and you've noticed weak points in the market on Youtube, Twitter, and Facebook. Analysis suggests you could sell 3,000 a month.

There's a lot more to it than that, of course.

Essentially:

Look at the competing markets, and based on all your analysis, try to figure out which one is the best allocation of time and money. In the end, only you can answer that one. I could give you hundreds of niches that I like, but they may not be right for you.

I doubt any of that has helped hugely, so let me finish with this:

If you're new to internet marketing, start simple. Go for an easy to sell offer (either low-ticket or an email/ zip submit) and work out how to present the offer and how to generate traffic for it. Easy to sell? We're back to competition. Look at the different sources of free and paid traffic. Do you see any weak points? If so, how much traffic do you reckon you can get? What's the average EPC of the offer? If you sent X amount of traffic, what might you be earning each day? If you're looking at ranking keywords (pages, videos, whatever), go for "buying keywords" / "action keywords" not lookey-loos. Think in those simple terms for now, just to get some experience under your belt, and some money earned. Then begin to delve into the fun world (LOL!) of niche marketing.

GRM

If I am planning to go for a long-term income then I am trying to get a broader domain name and split my posts into longer keyword phrases that would be able to rank easier.

For example let's say that you have the rocknews.com domain. You can now write posts about all genres of bands, being metal, softcore, metalcore etc... if your domain name is deathmetalnews.com then you have less choices. it really depends on what you love the most and what your aim is.

but my humble opinion is to get something broader and focus on keywords that can be ranked easier.

If I am marketing especially online marketing then I'll go for a specific rather than broad niche unless I have a lot of resources and money to spend on ads and building value for my brand.

It's easier to build your self on a specific niche. A niche which has low competition, and one having demand.

If you're running a small business then target a specific niche.

I would say that the answer lays within the experience and ability you have. If you are new to Internet Marketing, I would suggest you niche in pretty tight. Once you understand how things work together, how to develop a funnel and collect e-mail address' and in general how to actually sell stuff online.. you can widen that scope up a whole lot.

I personally focus on "Markets" and segment many "niche" targets out within the same site. Using your example I would build a site around "Windows" and then segment target "energy efficient windows" and "Low E windows" and would target "replacement windows" "energy Star" or "Argon" and so on and so on.

Like I said the market targeted type site is just not for someone starting out. And if you are not comfortable with all of the mechanics of a successful web based business, you simply will be spinning your wheels in 30 directions and more than likely not gain anything out of the process.

I would say you would be better off using energy efficient products as that would literally give you 100's of products that you could write articles or do reviews about & would eventually become different sub niches anyways. The only problem with being super specific is that eventually you are going to run out of things to write about.

Niche' marketing can be different depending on who your market is.
My market is direct sales people and network marketers which I can market to the same way through out the year.

But some of my clients have different niche' markets depending on what they are selling from their product line that day. For example - skin care products - You wouldn't try to sell wrinkle cream to an 18 year old or acne medicine to a 70 year old.

You can have several different niche' markets within one product line and have to define the best way to market each product.

My advice is to pick 1 item and the niche' market and begin selling. Then add another product and niche' market to the first.

Based on your audience targeting.
I think you can think of focusing on what your customer want. Or else, focus on what you can give them (your products/services).