Bishops and Knights

Ever since working on my openings, I've found that what used to be my main problem (allowing the opposing Queen to slip on by and thrash my pieces) has become less of an issue for me. Lately, it's become giving a Bishop away too easily (though I wonder if it's too easy when I'm taking out the oppsoing Queen early on), or allowing a Knight to be taken by an opposing Bishop. I'm having some difficulty managing this; I really don't like to let my poor Knights get captured too early in the game. I'm also castling as early as possible to get my rooks lined up for when the endgame approaches. Until I solve this current issue of endangering either (or both) my Bishops and Knights, this won't do me a whole lot of good. Luckily, I was able to download some chess help books from iTunes (and they were free; horray!). Hopefully they'll be able to give me some insight on my current obstacle.