One of the most common questions I get asked is how to connect the braid main line to a monofilament (or even fluorocarbon) leader material. I usually respond with a double uni knot (uni to uni knot) which is suitable for most fishing situations, but if they are truly serious about fishing they should learn the bimini twist knot coupled together with a lesser known knot called the bristol knot. The reason the bimini twist is recommended is that is created a loop or doubled line, which gives tremendous strength to the connection.
To make it easier for all of you I found a great video demonstration which shows one of the best methods for attaching braid to a monofilament leader. In this method the instructor the video uses a bimini twist and a reverse albright (also called a worm knot), which provides a strong, worry free connection.
These knots are slightly more advanced and can seem very complicated, but it is certainly worth the trouble and time taken to learn these fishing knots.