David Arora's "All The Rain Promises" is a good field guide, but his large "Mushrooms Demystified" from which the info in the former was drawn is mush more comprehensive (haha).
After several years of amateur enthusiasm for fall mushrooming, I can give you a couple salient points that may help:
-Picking mushrooms does not necessarily negatively affect the organism (which could be made up of miles of unseen mycelium. the root-like part that makes up most of the organism). The mushroom "fruit" is the mechanism whereupon it spreads it's reproductive spores. Picking and handling a mushroom may actually help disperse those spores to new environments. Picking ALL the mushrooms in a local environment would have the opposite effect (more on this below).
-In BC, there may be up to 30K species of mushrooms, with perhaps only a quarter of those scientifically described, and the vast majority of these easily falling into the LBM category (Little Brown Mushroom. Yes, this is a real thing). Most of these LBMs can only be reliably differentiated under a microscope by their spores.
-Of the minority of recognizable described species, perhaps 8 (from memory) are deadly and NEED to be memorized (as well as their look-alikes), several are not deadly poisonous but perhaps would cause varying levels of GI distress if eaten(up to severe, perhaps with certain food/drink combinations such as alcohol), a dozen or so are choice delicacies and should be noted, and a few dozen are not known for being edible but are interesting for other reasons (depending on what you think is interesting in a mushroom).
-There are no tricks that will help you identify if a mushroom is poisonous (such as "A poisonous mushroom will tarnish a silver coin", or "It's only poisonous if it has spots."). Old wives tales should be suspect.
-BC Parks does not allow mushroom gathering. I used to wonder why, then one day when I was walking to Cheakamus Lake I met an "expert" hosting a group mushroom forage. They picked every mushroom they could find, whether or not they had 30 of them already, whether or not they were of interest or not. Most were discarded in a pile at the TH. Not only does this affect the reproductive cycle, but seriously affects the enjoyment of other park users (insert "off-leash dogs on trails in Parks" analogy here). Rangers DO enforce this.
-Mushroom Festivals are a great way to meet real experts and fellow enthusiasts.
http://www.whistlernaturalists.ca/?page_id=20