What is the best way to prepare for an interview in Web Development?

You need to prapare you self HTML / CSS HTML5 CSS3 JavaScript HTML DOM jQuery AJAX JSON Google Maps The most improtant thing is that you fully understand the concepts of Web development , OOP Then the server side language such like PHP , ASP.net etc

You need to prepare yourself depending on the Job Position you will have interview in whatever programming languages, tools etc...
Ofcourse when you apply to a job application you can see that the employers list the skills/requirements that they looking for, when they call you for an interview to this position then you will need to be ready in these skills and requirements whatever its.
After all employer called you because they see that you may fit to this position and need to make sure about your skills.

you should read about oop(what is oop? what is used for? what are functions, classes, access modifiers and data types? waht is the benefit of using functions? how can you connect to database and read data from it?) ,sql(sql statements, stored procedures) ,ajax(what is ajax stand for? what its used for?) ,html, css, javascript, jquery(what is jquery) these are the major things that you should be prepared to answer any question on it

Giving interview is an Art.
Interviewers are usually rely on Behavioral Science for judging interviewees.
Mostly every type of interview remains same except some targeted post specific questions, as you've mentioned the "Web Development" here.
Remember: 1.
Web Development is not only a concept, it is a visible product anyone can see.
So first you have some very good stuff to present as your portfolio.
Good memory can help you to memorize many technical jargon easily, but the matter is not to memorize those, it is how you implement those and gather that knowledge as a useful product.
So the employer will always need to see some of your past work.
The most important thing you've to get prepare for.
2.
Never try to explain those things which you don't know.
Yes! you can elaborate the other tools or technologies to perform the same task on which you have good commands.
3.
You must be aware of all job requirements mentioned in the job opening.
Usually companies mention two types of prerequisites one are the necessary second are the options or preferred.
You can go for an interview if you know the necessary elements but not good in optional ones, but don't waste time if you are not even fulfilling the basic prerequisites.
There are many other variable things which will depend on job requirement and company requirements.
But again the main thing which will work is your confidence and passion towards your work.
Here are some links which will always help you getting ready for your interview.
The 2nd one is specifically for Web Development related job Interviews : 1.
http://ebydavid.com/wp-content/uploads/2010/01/64-interview-questions.pdf 2.
http://ebookbrowse.com/web-development-interview-questions-pdf-d17414351

Try to find out if you can what kind of technology they use, php, asp.net, java etc.
Try to read a bit on frameworks related to such technology; Drupal and Joomla for PHP, MVC for .NET, etc.
Also, it depends on what the position entails, would you be working on backend code, like creating classes and stuff, then you want to know about OOP, design patterns, etc.
If more on the front-end, then you would want to concentrate on HTML, CSS, and Javascript.
Also, some of the front-end frameworks, like jQuery and Mootools for JS, SASS and LESS for CSS, etc.
Good luck!

First follow the JD & study the topics mention in JD that can be your best approach to prepare accordingly most in minimum time, mostly interview in UAE & gulf pretty straight forward so just belive in yourself & confident.
I accept its more on your behaviour & attitude Don't forget to ask to the question related to company profile & job to interviewee at end of the interview.