Tips on buying a beginner mountain bike I hope this question isn't too subjective or open-ended, but I would like to know what I should look out for when buying a beginner mountain bike.

My aim is to ride off-road and downhill tracks, but I don't know what type of bike I should be looking at.

Should I look at a hardtail or do I get a second hand full suspension bike?

Are there specific brands that I should look out for or stay clear of? 

Any other tips that you might have would also be greatly appreciated.

EDIT

As per the comment below I am adding some more details.

The trails that I am looking at is more the foresty type single tracks. The way I am going to get to the top will be to take a back-route that is more open view. 

For all intensive purposes the forest scenario will be ridden the majority of the time, but I will surely do open view rides as well.

EDIT 2

With the current exchange rate as it is I would say that my budget is roughly in the $1000 range.
At your level all brands are equal and you can find a suitable bike for yourself in almost all brands. Focusing on a specific brand will only make it easier for you to choose but don't, for one second, believe that you've found a better brand than others.

I suggest visiting a couple of LBSes (local bike shops) to get more info and test ride a couple of bikes (even in the parking lot). Pay attention to sizing. This is something that your LBS will help you with.

If you need a bike for getting stronger and having a bit of safe fun then any $1000 26 inch XC hardtail with 100mm front travel will do the job. The bike will take you anywhere and will last for decades.

If you feel that at some point you'll want to get more aggressive then you'll need a more aggressive hardtail with slacker head angle and around 140mm of front travel.