The team (or person); the concept; the market; and implementation.

Have you read this article by Paul Graham? You can't tell if a startup will be successful, in my opinion: the best you can do is your best, and work up from that.

• Is it going to make more money than it costs?
• Is there a single person making all major decisions?

I think everything else follows.

It all starts with the team behind a concept. If there is no passion in a team it will absolutely fail. Also check their background. Have they already succeeded in some way before?

What market are they trying to reach. If it is a niche market with big potential or a new fresh model in a crowded market, investors will be more likely to invest/participate.

After that I would conscider the businessmodel (are these guys able to generate money).

How are they spending their money. If they are spending money like a can of water in useless things, investors are not likely to participate. They want to make money... not wasting it :)

Passion, Perseverance, Execution and Team! If your startup is solid in all four of these domains, I believe you will be successful.

However, another critically important factor is flexibility. You have to be extremely flexible and be able to adapt to what your users want. Because at the end of the day, they are the ones who will pay for your product/service.

This is what I think:

If you don´t have a good idea forget about it.

Ask some experienced entrepreneurs if they think your idea is good.

Try to think how people getting your service are gonna feel.

Imagine that you are getting the product you want to sell.

Then, if you are short on cash you need some investor. Don´t ask for a loan unless you are 200% secure about your succeed (BE REALISTIC) Make sure you gave a B, C, D, ..., Z plan.

Add water and enjoy.

Team.

Of course I will look at their skills, but more than that I would focus whether there is love and respect between them. Everything else (concepts, marketing etc) will automatically follow. Trust me.

I would like to give you a link but since you want opinions this is what I think. I believe there are essential elements to decide if a startup is gonna succeed or not like:

The fact that you need to have a well planned, realistic, and anticipatory STRATEGY. In this way you know what to do, how to do it, and how can avoid potential problems.

That is why you need to design a the your OPERATION processes and TACTICS. It is vital for any business to know how to get it done.

Finally, you need to hire the right People in order to making it happen.

P.S. Money