I'd like to disagree though that bad spelling and grammar is an obvious sign of badfic. Though it certainly isn't a characteristic of goodfic, I don't agree with the implication that only fic with bad spelling and grammar is sporkable. I've PPCed a few fics that actually had excellent spelling and grammar. I even complimented one of the Sues on this (after the charging she asked: "Wasn't there anything you liked?" The charging agent replied: "Your spelling was good.").

For me an obvious sign of a badfic is a plot that doesn't work, because it is contrived, or because all the canon characters seem to be replaced by wax statues or cardboard cutouts.

The most obvious sign is that I am making riffs while reading it for the first time. That means a story is bad and it means I can be funny about it. There's no point in writing a PPC mission if it's not going to be funny.

There's no addition procedure. I often (but not always) review the fic before I PPC it, pointing out some of the issues (not all, because you'd be left without material for a mission and you'd overwhelm the author). If and how the author responds is not really important for how I proceed. Unless that respond is: thanks, I will rewrite completely. I've only had that response twice on a review, once for a story I wanted to mission. I asked that author if she was okay with a PPC mission of the original story. She had to think about it, but after a few weeks (by which time I had already written the mission) she said "Okay". Incidentally, I didn't kill that Sue; I let her die of the injuries sustained in the story, but with her admitting she had erred.

I used to notify authors before posting a PPC mission. Just a friendly message that I wrote a spoof about their character and if they felt personally attached to that character they probably didn't want to read my story. I post on FFnet so it's relatively easy for badficcers to come across my sporking of their fics. I stopped doing that a while ago. I think it's because I wanted to notify someone that turned out to have me blocked after a review I left. Interestingly, this author put up an author's note on her latest chapter saying I should have contacted her about posting my PPC mission. (Mind boggles)

Others will probably advise you not to notify authors in advance to avoid flame wars, but I haven't actually ever been flamed by any of the badficcers. So, it's really up to you whether you send the author a polite message or not.

You popped in and then vanished for a while! Like I did when I joined!

Here, let me link to you some things of interest that should answer any and all questions you may have. The wiki is not our SOCIAL hub, but it is our archive for documents and such.

FIRST: Da Rulez, if you haven't read them already.

Guide to the PPC

FAQ for Newbies

Permission

Mission Writing Guide

Slash-Sporking Guide

Posting New Mission Reports

This may seem like a lot of reading, but it's really not. A lot of these links are somewhat redundant, for they're all guides others have written at various times.

And don't think these are all some kind of strict rule code. The idea is that we follow a certain spirit and basic protocol when getting Permission, facing badfic, and publishing our work as to make it as pleasant as possible. Whether this is by avoiding conflict with a badfic author, promoting harmony in the PPC itself, or simply writing in the spirit of the PPC, we're a peace-loving bunch. We're here to have fun, not restrict or belittle others, above all.

Welcome back to the community! Glad to have you. :)

I wasn't here back in April, but welcome back all the same. ^^

As for selecting fics, it is very much a question of personal preference and taste.
Besides horrible spelling and grammar, things you can look for are canon-breaks, out-of-character characters and Sues. The wiki [light shines down and a choir of angels is heard] has this entry on badfics, http://ppc.wikia.com/wiki/Badfic you can check out to get ideas.
You should however first and foremost look for something that can be sporked in a funny way. When you read a potential badfic, you can try MSTing for yourself and see if it gives you any ideas.

As for your questions, we do not notify the author, neither before nor after we spork their fic. It is considered something like a personal attack on the author, and besides it attracts whiners and flamers and we don't want them.
If you want to give them a helpful review before sporking, feel free to do so, but it is in no way required. Also, for truly terrible badfics, it can be impossible to give reviews, that isn't simply: "Oh god, the stupid! It burns!"

Hope this was helpful; otherwise feel free to ask again. There are wiser and more experienced persons than me who can help out.