In the quest for determining value, you'll first need to get your album cleaned up then grade it. Here are the steps for doing that:
*Clean albums (see "How To Clean Your Vinyl Albums").
*Holding album by its edges, examine playing surface, label, inner sleeve, cover and inserts (posters, lyrics sheet, etc.), looking for signs of wear.
*Make a determination based on the following grades:
Mint (M) - An album perfect in every way, never played, often still-sealed.
Near Mint (NM) or Excellent (Ex) - Almost perfect, showing no signs of wear. Label, sleeve, cover and inserts should also show nothing but slight handling.
Very Good Plus (VG+) - A few signs of being played, but was well cared-for. Very slight surface scratches that don't affect sound. Label, sleeve, cover and inserts may have slight ring or handling wear.
VG+ is worth approximately 50% of the Near Mint value.
Very Good (VG) - Same traits as VG+s but more pronounced. Slight surface noise evident. Light scratches may affect sound. Label, sleeve and cover may have writing on them or tape residue.
VG is worth approximately 25% of NM value.
Good (G) or Good Plus (G+) - Will play without skipping, but has significant surface noise and scratches. Cover and sleeve may be split. Writing, ring wear and other defects may overwhelm album.
G or G+ is worth approximately 10-15% of NM value.
Keep in mind that other factors besides grade will affect the value of your album: artist, rarity, and supply and demand.
*After grading, gather prices from several different sources and use their average to determine the value of each album.