Unless you have something unusual about your situation (e.g. criminal record, extensive stays outside the US, etc), it's dead simple.

And if you've been in the US for 10 years, don't apply under the marriage path of 3 years residency, apply under 5 years. They basically verify you've lived in the US for 5 years (you have records of all your international travel right?), aren't a criminal and boom approved.

The marriage route is a bit more complex as it can involve legitimacy of the marriage (although not much of a hurdle for most).