Dan,
Let the rubber overhang the ends of the channel by a quarter of an inch, this will ensure you remove as much water as possible from the window frame.
Not all channels require end clips, most of the modern squeegee handles grip the rubber in the channel.
Out of preference i use clipped channels as it keeps the rubber tight and level, but its all down to preference.
Another tip for you is to make sure the rubber is cut square and neatly, the slightest burr will leave lines in your handywork. To cut rubber neat every time i use a pair of Anvil type secateurs.... works a treat.
Hope this helps
Denzle