What do potential customers look for once they land on the homepage?

If a potential customer visit to a particular website, what are the things he will check,
1) What is the page rank of the website
2) what is the competency of the company
3) How much clients company is having
4) what is the word of mouth or third party review on the company's product.

A potential client is called potential because they're in the market to buy a product or service that you're offering. When they come to your landing page, they're looking for a solution to their problem and some proof that your offering works. The proof can be in the form of links to 3rd-party reviews, existing customer testimonials, or mentions of some big-name clients. Most importantly, the copy must be written in the terms that your potential customer understands.

As for the options mentioned by the OP:

1. Nobody cares about your Page Rank.
2. If your potential customer comes to your page not knowing what you do, that's not a potential customer. And if you don't say what you do on your landing page, you aren't doing it right.
3. Nobody ever discloses their entire client list.
4. Word of mouth has no place on your official website because that's what brings potential customers to you. You not only can but you should link to 3rd-party reviews.

If they're already on your home page, they are looking for reassurances of 1) Trust & Honesty, 2) Ability to complete a task with the highest possible proficiency and on time, and 3) Straight forward and simple methods through which to communicate with you. Everything else (customer reviews, portfolio work, your branding, your page rank) are only clues to your standing in one of these three areas.

A home page should be simple, clean and confident; after all, they've already spent time and energy to visit your site to begin with, now they just need those ever important reassurances.

When a potential customer comes to your web site they are looking for a solution to their problem. Always keep that in mind. You provide a solution in the form of a product or service.

Your web site should be targetted at providing your potential customer with enough information to make the buy decision. So what does your customer need to make that decision?

1. Your potential customer doesn't need page rank, and I doubt if 1 in 100 consumers even know what that is.
2. Your potential customer would like to know how competent your company is, but how will you convey that information to him or her?
3. A client list may be of help, but it is not the primary, or even secondary point of the web site.
4. User reviews might also be of use, but once again they are not the primary or even secondary thing your web site needs.
5. Your potential customer does need enough information to make an informed buying decision.
6. Your potential customer does need an easy and obvious method to buy your product or service.
7. Your potential customer might need a way to try or demo your product or service before buying it.

Don't forget to make the contact information easy to find. Being able to see who is behind a website and where they are located etc helps a lot with building trust.

I know I look for recent blog entries and/or informative articles if I am considering a product or service. A stale template with vestiges of Lorem Ipsum (or just the bare minimum info) and a 2008 copyright would be a red flag to me. For example, a hosting provider should have good information on FTP for beginners and creating an SSL cert for more advanced users. A support forum that is easily accessible from the home page is nice too.