seychelle "What are the essentials that I must look for in a bike frame ? material it's made from, weight ... ?"

fit, fit, fit....and did I mention....fit? Oh, and it also has to fit you

In your price range don't worry about weight. Remember only about 1/5th of the weight of the bike is the frame anyway.

Buy the bike that fits you best.

Over time you might upgrade it (lighter wheels is the most effective money you can throw away at a bike). Many here find your first bike ends up being the winter trainer/commute'mobile and you might buy a lighter bike for longer rides.

All things being equal if choosing between a couple bikes and they both fit and are about the same price...look for the best groupo, that's quality components like Sram or Shimano for example.

Over the years and many happy safe miles you'll be replacing the power train (deralieurs, brakes, crankset, chan) anyway. At that time you may go for the next model or two up and voila! Lighter bike.

You're "stuck" with the frame, it must fit you. The most expensive bike you could buy is the $___.__ bike that sits in the garage because it hurts to ride.