Watch the Fills and Hooks online guitar lesson by Jason Loughlin from Country Guitar Survival Guide: Rhythm
Fills can add excitement add movement to a rhythm guitar part. Any kind of lead approach can be used as a fill. Chicken pickin', bending licks, blues licks, double stops, lap steel voicings...all depends on what style you're playing and what vibe you want to evoke. As a general rule you never want to step on or distract from the the vocal. You can save your fills for the end of a phrase or to help set up a chorus, bridge, verse or ending. You could fill around the vocal. Just make sure they are adding to the song and vocal performance and not taking away. Now you may not be the only instrument who can fill. You might be playing with a steel guitarist, fiddle, piano or all the above. You'll need to work out visually who's going to fill when and where. Deciding filling order can really shape the way a tune unfolds. If someone else is soloing, give them room. Be supportive. There's no room for egos. By making a fill a reoccurring idea you're establishing it as a hook. Hooks can act as intros, outros or interludes. Hooks can also act as a response to vocal phrases. Listen for them and analyze how they're used in your favorite country tunes.