Extra pieces in a lot, not sure what to do with them
Yes there is. However, it requires two pieces of knowledge:


You need to understand how BrickLink or BrickSet categorize the 10,000+ types of LEGO bricks in existence. This means knowing the difference between a Brick, a Plate and a Tile, understanding the various Modified versions of these basic types etc.
You need to be able to identify pieces in your stash of bricks that are special or not commonly used. The best candidates are bricks with stickers, as stickers are often special to just one set. 


Once you have identified one or more unique pieces, look them up and see which sets they came in. Look through the inventory of those sets to confirm you have most of the other pieces in that set as well, and voila: you have found your set.
Next, go to www.lego.com and download the instruction manual for that set, then build the set to verify its completeness.

Note: if one of the stickered pieces contains a car license plate, or any other sticker with a 4 or 5 digit number on it, chances are that that is the set number. Then just validate that other pieces from this set are also in your pile of bricks.