It is helpful to understand exactly what it is your are looking for.  The cache size will let you know in general how large the cache container is to be found.  Here are some guidelines for the icons that appear on the search page.

 Micro - This is a very small container you are looking for.  It could be a film cannister or a specially designed key ring cache container.  Either way, you need to stand still and slowly look around for these.  Be aware, they also make hollow rocks now !

 Small - While these containers are larger than the Micro they are still easy to miss.  A good example of this size container is a waterproof match casing or a small tupperware container.

 Regular - These size containers should be easier to see with the naked eye.  Typically they are ammo boxes or "decon" containers.  Given the size of these containers, there is usually some thought as to the placement of the cache.

 Large - These size containers are not that common.  Just think larger than an ammo box.  Maybe an entire tree stump that has been carved out?

 Unknown - This "size" container is usually associated with the Mystery type cache because the owner does not want to give away the size of the final container.

Always read the cache details which will often specify exactly what the container looks like, including its color.