Oolong loose tea is as easy to brew as any other type of loose tea.  You should use filtered water for your tea and make sure that the water reaches 200 degrees Fahrenheit.  Do not over boil the water because a higher temperature could burn the leaves and ruin the flavor of the tea.  You then add two teaspoons of tea to six ounces of water and let rest for three minutes.  Instead of increasing steeping time, you should use more leaves if you want stronger tea.

I made some Oolong Loose Tea but it was very weak

Many people think that if you want stronger tea, you should let it steep longer.  This is not the truth.  You should simply add more leaves to get a stronger flavor.  If your tea was weak, you may have used too much water or the water may have been too cool.  You could also be using the wrong type of measurement.  Tea should be measured in heaping teaspoons, not level.