Just a couple of comments from someone who has quite a bit of experience with what your are suggesting in your first couple posts (albeit that was quite a while ago before I learned how to trade options more efficiently).
More often than not the IV is over-inflated before the earnings announcement. IOW, for the most part, a straddle purchased within a few days of the ER will be a losing trade. It will be VERY difficult to have consistent success picking tickers that will move enough to offset the IV collapse.
On the other hand, you could do what has been suggested here and purchase the straddle a couple weeks before. In my experience this is also a losing trade as you would really only be buying the front month options and theta will have killed you by then. Also, you will probably have moved away from the strikes that were originally selected so you are no longer delta neutral and if you want to balance back out before the ER you will have to make an adjustment, usually at a loss.
If you choose not to make the adjustment and remain unbalanced, there is a high likelyhood that the underlying runs one direction before ER and then reverses the other direction after ER. In this case you get screwed to say the least.
Purchasing the strangle does decrease the odds of success. Actually, the strangle is more of a lottery ticket than anything else.
What it all comes down to for me, the only way to really make consistent money buying a straddle is to do so a couple weeks before the announcement looking for the IV increase into the ER and then sell the day before the earnings are released. But it seems you have very limited knowledge of IV so this would also be very hard for you to do.
I would suggest staying away from ER until you are much more familiar with the greeks and option pricing.
