I think God-modding isn't really a hard and fast set of rules. The truth is, it's fun to have player driven content and to build some things around your character that is fun to experience. God modding is almost certainly situational, and avoiding it is driven by the following question, "Does this make sense if I'm totally honest with myself?"
As an example, I'll take Constantin Baracca's current ministry. He is traveling the cluster with a few other priests and they are working to convert people into the Amarrian religion. He literally talks about a vast number of people he's converting and that he's starting a movement. That's a big pill to swallow, because that's a huge chunk of assumptions to make. However, this has happened in real life and has historical precedents. To make this palatable, though, you have to ask a few questions and you face a lot of restrictions.
- Would this work in real life? Obviously, Father Constantin has to be focusing on someone who is not happy with their lives. He is essentially selling slavery or, at the very least, an undeniably authoritarian government. So would he be able to convert thousands of well-heeled middle class or rich people? Obviously not. He is going to have to start converting people who hate their current society and are willing to believe that ANYTHING is better. So Constantin's converts are usually lower income or completely homeless and unemployed. Most of them are recovering drug addicts or prisoners who can't find satisfying work. This plays back into Constantin's character, making him into a charitable champion for the impoverished, in his own way. This also avoids people with real political and monetary power being largely involved.
- Would someone have rationally interrupted him by now? That's probably the most important question you have to ask before you fire a gun at everyone in a bar or walk into a Matari government hall with a train of slaves on a long chain. You have to have an answer for this or just don't do it. Constantin doesn't often dock in Minmatar space and has to do a lot to cover his tracks (you guys don't even know the half of it). However, since he does tend to shoot pirates in Minmatar space and isn't necessarily seen as much of a threat, he is tolerated, if not welcome in their space. I have to keep in mind, during his RP, that Minmatar space especially is a very thin line to walk for him. Other spaces have no issue with him at present, but Constantin can't get too crazy out there or the government will make sure he can't even jump into their space.
- What needs to happen for this to be possible? Constantin has to have the backing of the church. Amarrians in general don't do these kinds of things solo. That means he is definitely working for someone with the blessing of very powerful people. I have to keep that in mind. If he'd done this shtick and then I'd made the claim that he was fighting the church itself, it wouldn't make any sense. So it's important that, even if he doesn't talk about it often, it's known he has backing.
- Can he be stopped? In your mind, you need to know your character isn't untouchable or unbeatable. That's almost a given, since a character needs to minimize his vulnerabilities anyway if he wants something to succeed. Constantin can be interrupted or stopped, but someone would need to work very hard. He's something not often seen among capsuleers: a charismatic preacher. Lucky for him, he's not exactly running into people who know how to deal with him.
This is in a general character-defining sense. Essentially, almost anything will be allowed if it is interesting enough, but it has to pass what an old RP tutor of mine called "the smell test."
For example, let's say a fight breaks out in a bar. You post that you turn towards someone who is backing into a corner and do whatever it is you do. Someone behind you says they pick up a chair and swing it at you while your back is turned. You almost have to allow the hit to stand because, by definition, you can't see it coming and you have no way of knowing when it hits you. If it does, you can almost certainly roll with it. If you're large, you can macho your character up and have him shrug it off. If in the past the person hitting you with the chair talked about wearing high, clicking heels, you can say you hear him coming. Or if it is a woman who has described she is wearing a certain scent, you can smell her.
At the same time, an attacker has to be realistic. The person with the chair needs to be very specific with what's happening and what the circumstances are. If the attacker is a five foot, ninety pound woman, even a chair probably isn't going to send a seven foot, three hundred pound behemoth of a man flying across the room. There is a reason large boxers have their own weight divisions, even a few pounds and a few inches difference skews a fight's favor monumentally.
Most of all, be reasonable. There are less people who go to bars specifically looking to fight anybody at all than you might think. No one is walking into bars and immediately splashing a drink into someone's face for no reason. Even if that happens rarely in the real world, it isn't really making for interesting RP. It's about to start a conflict without any investment. Suddenly, two people are trying to hurt each other and there's no reason why anyone should be interested in the outcome.
Sometimes, you just have to realize that RP isn't exactly like RL and we're here to tell stories. Things should happen that drives character development and story development, not bring the flow of the evening to a screeching halt. Any fight will inevitably do just that. If most of the people in a room are ignoring a fight, odds are they're ignoring your RP for a reason. That's not usually something you just miss. It might just be that people are starting to think that, rather than a sudden breakdown due to tension, this is just someone IRL interrupting their much better and personal RP.
Hence the "smell test". If people look at it and think it's genuinely character driven and rational, people won't call you out on it. When people are calling you out on something, even if you don't think it's god-modding, you have to realize you've set off the smoke detector somehow. If it doesn't smell right, people have a right to call you out on it. While it's fairly obvious that having a bottle of expensive cognac isn't god-modding but having a cadre of ninja warriors suddenly attack the bar Dusk 'Til Dawn style is, sometimes you just have to use your best judgement.
I'd say that the best thing to do is to make sure other people are involved and that everything fits in the flow of the roleplay. If you spend enough time setting it up and EVERYONE is really enjoying kicking the shit out of your ninja NPCs, even that's not god-modding. If you suddenly produce a bottle of fine cognac while you're locked in a prison cell with no way out, you've essentially auto-ed in a non-apparent element.
There are comprehensive lists and ways you can go about defining what is and isn't god-modding, but there are really no hard and fast rules. Given time, circumstances, and everyone's approval and involvement, you can get away with almost anything. If you don't bother even pretending you're just one character in a world instead of Duke Nukem in a field of bowling pins, everything you do is going to be god-modding.
Regardless of what people outside the gaming community think, RP is all about social skills and interaction. The skills that make a good RPer aren't the ones that make a good writer, they're the ones that make a good team player. It works best when you play as one element of a world. Let other people make a big deal out of you or not. Odds are, if your character is good and your RP is solid, people will want to interact with you. You will give their character fuel and a lot of room to flourish. Don't dictate to the crowd if they already don't want to be sitting down to listen to a speech. They'll not be paying attention and you'll only be interrupting their conversations anyway.