which technology or strategy a new / inexperienced freelancer should use to earn profit?

First off, I like PHP & MySQL. However I think you should work with what you already know.

In my experience the best strategy's in your situation are...

1. Get a down payment, some % of the total cost you will be paid. Then show the client the completed work and get the rest of what your owed before handing over the code.

2. If the first option is not possible, work on the project but always have a back-up plan of what you will do if you do not get paid. I always keep back-end entrances on my site which allow only myself to enter a clients site. If they were to rip me off I would be able to take down the website. If you don't want to invest in making a program or script to do something like that, simply with hold the code until you get paid.

PhilipK is right: I've been taken for a ride, I've lost $2000. So now here's how I do:

• rule #1: never ever ever trust clients. Nowadays, money is often more important than anything else. So be warned: many clients may try every possible things to see how far then can get with you for free.
• Now as for the contract: 30% of the total cost first. Don't worry: if the client doesn't want to pay, find another one. If you're good, or if you believe in you, you will always do the job and find a client that is willing to pay. Don't hesitate with small jobs.
• then define 7 steps: and 10% / each step; maybe you could change (that's what I usually do actually) 2 steps: 35% first, 35% for the last one (where you give your source code)).
• the only hard stuff is planning: just imagine how long it will take to make that, then multiply by two and you may be close to the reality. No kidding at all.

Once again: whether you're a beginner or not, just think that you're always worth something. ;)

To add one thing (after your comment): I was thinking like you a few years ago i.e.: "if I've lost some money (or if I'm underpaid) that's not a problem, because my work isn't that good". Here's what happened: you've learned a lot between the start and the finish.

So now that you've learned a lot, you find your work to be not as good as it could be, and you feel guilty about that. You are wrong. In computing (maybe everywhere else (including relationships)) you always learn a lot and if you look back you will always think your work isn't very good because now you can do better.

Knowing that, keep in mind:

• your work is always worth something event though it's not the best you can do;
• you always have to be paid for a work. Period.

Good comments thus far. If you are looking to learn a new technology for the web I would suggest Ruby on Rails versus PHP. I started with ASP, then did PHP, then ASP .NET and am now doing Rails and it is amazing. Also tutorials online and books you can follow to get started with it pretty quick.

Other suggestions:

• Collect an initial payment up front
• Deploy to a development server that only you have access to. They can test it but not 'steal' it or take it without your approval
• When they eventually want to go live and launch then make sure they are paid up before hand -It sounds like you are pretty new to web development, so there is also some risk on your client's end that you might not be successful with the application. You should also consider that possibility.
• You should draft at least a basic contract / agreement of expectations of features, deliverables and payment.

Final tip. If you don't trust them don't do business with them. Why would you want to? Always trust your gut, it is usually right.