I recommend watching CAD (CL usually leads first) because of the amount of Canadian exports relying on oil. Also watch the US Dollar index, because since oil is priced in dollars a stronger dollar means oil lower (all things being equal). Think of Oil almost as a currency in itself for that purpose as USD:CL.
Finally, making no assumptions about your skill level, you might also want to watch the price on multiple delivery contracts instead of just the forward month. Remember, the majors aren't playing in the forward contract, they're all dated much further out, so option pricing there is much more meaningful.
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