For 2014 I made a resolution not to start any book series that wasn't completed (any series I had already started didn't count) and available in ebook format at a reasonable price. It's a resolution I've kept since 2013 but I won't be continuing it for 2015.
There's no particular reason for this, I don't feel the need to hold myself to it anymore. Any completed series will still take preference on my to-read list but I can allow myself the odd exception, probably starting with Brandon Sanderson's Rithmatist!
However there is still one thing that will make me drop a new book series until it's completed. Cliffhanger endings, they are a pet peeve of mine I even avoid season finales for tv series (until the next season airs) as they inevitably setup a climax that won't be resolved until the first episode of the next season.
If the first book in a series ends in a cliffhanger I'll stop reading until the series is completed as I assume that each subsequent book in the series will end that way and I really don't care for the wait to find out how it's resolved.
Anyway I hope anyone reading this has a happy 2015 filled with lots of good books!