What rules should I follow for improvised food recipes that aren't dangerous?

I've never heard of any two things which are safe to eat separately, but poisonous when combined. When you consider everything gets mixed in the stomach anyway, I find it unlikely to ever find things like that.

Daniel's question about your food safety knowledge is an important one. Make sure to use separate tools for raw meats, clean your tools, cook to appropriate temperatures, and not leave food out either thawing or cooling. I wouldn't feel bad if -everyone- took a food safety class at least once in their life. I mean, it's typically a few hour workshop.

In the long run, I would encourage you to aim for a diverse diet. Make sure to include starches, green and root vegetables, and other oddities. The underlying attitude of "I'll eat whatever is quickest to throw in a pot" can lead to frequently finding the same thing "quick to throw in a pot" and a less healthy diet.

As long as you are following food safety rules, any standard grocery store ingredients should be fine. I can't speak for exotic foods.

Possible problems:

1. You may have digestive problems if you have too much/little fiber or if you overload it with chile. Nothing dangerous though, assuming you are in good health.

2. You may have long term troubles if you aren't getting proper nutrition.

3. I am assuming you aren't going mad scientist and mixing things like vinegar and baking soda and drinking it before it can fizz fully. Don't do that.

Make sure raw meat is cooked, vegetables washed... other than that... go nuts?

Ingredient combinations are rarely a problem. Mishandling ingredients could in some cases cause trouble:

-Putting anything that isn't supposed to be consumed raw, due to being unsanitary when raw (mostly animal derived ingredients - eg non-sushi grade fish, pork, chicken), on the plate raw.

-Putting anything that is toxic when raw or incorrectly prepared on the plate raw (mostly applies to plant matter - eg some mushrooms, cassava, taro, kidney beans, candlenuts, or unusually huge amounts of vegetables containing solanine, phasin or oxalic acid)

-Using parts of a plant or animal, bought un-pared, that aren't supposed to be eaten (eg the wrong parts of rhubarb).

-Using unfit amounts of (25%) distilled vinegar, pearl ash, lye or other ingredients with extreme pH values (it is likely that a dangerous dish would also be unpalatable).

-Using far too high amounts of certain spices - half a can of ground nutmeg or ghost pepper would probably not do you much good (but would make the dish obviously unpalatable).