I have only one firm rule in regards to animal rights: Do not cause unnecessary suffering. But I suppose the catch is what people would declare necessary or unnecessary.
Let's be clear: Nature does not give rights to animals. Nature KILLS animals all the time. Billions, upon billions of species have gone extinct, and that was before Humans even evolved. Nature didn't give a damn. Nature never does. Nature is mindless and random and simply does not care about anything, since Nature lacks a mind and therefore cannot care about anything.
Rights come from beings with intelligence. WE create rights. WE enforce laws in regards to rights. Don't tell me that humans are the cause of all evil - nature and the wild is plenty evil on its own. A lion eats a Antelope, a Snake devours a rat, a spider dissolves the internal organs of its prey, killer whales will occasionally kill penguins just for the hell of it (as do Polar Bears) and Nature is just... FULL of aggression.
Of course, that doesn't mean WE humans have to act like that - we have a mind, we have a sufficiently advanced intelligence to start to break free of the hold of nature. But let's be clear - we are the only creatures that can do so. All rights are created BY US and given BY US or taken away BY US. Nature lacks the capacity to even comprehend the very notion of universal rights - and certainly no animal has ever drafted a constitution or held a court. A pack of wild dogs would tear apart a human in a forest if they got the chance - this idea that somehow humans are violating the natural rights of animals by interfering with them is ludicrous - animals HAVE no natural "rights". Rights don't EXIST in nature, nature red in tooth and claw.
So humans determine what rights animals have. This has always been the case. In my mind, humans should strive to treat animals based on their ability to feel pain and their mental complexity as well as their lifespan. Obviously bacteria, despite being alive, are afforded no rights - they don't have brains or nerves. They can feel and think nothing. Protozoa, and insects, are similarly primitive - their minds are so minuscule and tiny that I sincerely doubt they have the ability to comprehend anything other than "lay eggs in rotting meat" and "move if something fast is coming towards you". If flies and ants had any real intelligence, I've seen no indication of it. I strongly doubt an ant or a fly has the ability to even form a personality. Certainly most ants are slaves and are happy being slaves to their Queen.
Lizards, Birds, Rodents - these creatures are more complex and live longer than insects, and are thus afforded more rights... but not much more. If they aren't causing any problem to human beings, then they should be left alone. But if they get in our way, if they carry diseases, if they keep on moving into our buildings - get rid of them. It's not like the Lizard's family is going to cry over it, or bury it in a cemetery. It's a lizard - it's mental functioning is two to three steps above a Roomba Robotic Vacuum Cleaner for god's sake. And sorry, but I never seen a Lizard show any great emotion. Do you know, they frequently EAT THEIR OWN YOUNG?! And engage in cannibalism?! They care so little for themselves - so why should we?
Higher order animals - dogs, then monkeys, maybe whales, and definitely dolphins all exhibit some degree of memory, personality and can express emotions. You only have to see an elephant commit suicide in a zoo to know that it can feel despair. These animals should not be harmed unless we have absolutely no choice - as in, if an Elephant is charging at a group of children, you'd have to shoot it. Otherwise, don't kill it under any other circumstances. These animals also tend to live longer - decades, or sometimes even longer than humans.
I put animals on a sliding scale. We, of course, occupy the highest rung on the ladder. Why? Because we are the only creature capable of self-improvement, dreams and science. No other animal can do this. And DON'T say "evolution allows animals to improve" - no it doesn't. Animals evolve due to nature - they've got no say in the matter and they don't consciously evolve. Plus, Evolution is only ADAPTATION. Not self-improvement. Animals actually don't have the capacity to comprehend creating something or doing something other than survive from day to day. Humans can comprehend, or envision, something better for themselves. We can envision rights, we can envision a point in time where we can build a better future. Animals can't.
Should we eat animals? Sure, if they're dumb. Chickens aren't very intelligent. Pigs... I'm not so sure. They've been seen to occasionally display remarkable intelligence. Cows? They're dumb, so dig in (I don't eat beef, only due to the health concerns of Red Meat). Fish? I've never seen a fish look at the stars and wonder what the future held for it. I've never seen a fish form a culture. So go ahead - eat it. Fish are dumb as bricks. If they were intelligent, you'd think they MIGHT have learned that "shiny hook with worm = bad"
Humans are the only creatures that have a CHANCE at avoiding extinction. Nature routinely kills of animals all the time. The universe certainly doesn't care much for life, if the amount of asteroid impacts that have hit the earth are anything to go by. And the sun will one day run out of fuel. Life on this planet is PURELY TEMPORARY. It has lasted billions of years and will last about a billion more (after a billion years the sun will have grown in size due to the using up of much of its fuel, so that Earth will become an uninhabitable hell like Venus).
Only humans can avoid this - nature has no conservation parks of its own. You don't see woodland creatures banding together to "Save the Buffalo". Nature DOESN'T CARE IF SPECIES GO EXTINCT. IT NEVER HAS AND IT NEVER WILL. Only humans can save life from inevitable extinction. Only humans have EVER GIVEN A DAMN about creatures going extinct. Rights, conservationism, ethical animal treatment - that's all our doing. Not natures. So since we are the genesis of Animal Rights, we have complete control over them.
So - eat the dumb animals, use animals for medical testing (not cosmetic testing) and avoid causing unnecessary pain - not death, only unnecessary pain. If you are going to eat a cow, more power to you, but make sure you make that cow die as quickly and painlessly as possible. No need to draw out the process. Cows and most other mammals and animals CAN feel pain - they have nerves and they'll sure as hell react if you try to stick a fork in em when they're alive. So just take that into consideration - minimize suffering where it is possible and convenient to do so.
The minute I see the majority of animals treating EACH OTHER with any semblance of ethics is the only time I'll ever even think about any sort of "natural" animal right.