I have two boys, 4 and 6.  When they were 2 and 4 it was especially hard because I felt more responsible to protect ds2 since he was still smaller and more vulnerable than ds1. It's easier now to deal with them equally since they are more physically equal.  We are definitely a work in progress, but things I have been doing that I think are good are:
- read Siblings Without Rivarly. I need to read it again.  Most of my mindset on this I got from that book.
- Don't solve their problems for them if you can help it. Step in and say things like "Oh, I see one flashlight but there are two kids who want to use it.... Can you guys think of any ideas on how to solve this?"
- Hear both sides of what is happening. It helps them know you're there for both of them. The idea is to keep their arguments to the issue at hand and not add in "competition for Mommy".
- Keep in mind that the younger kid can be an instigator - not always the victim.
- I try to tell them to deal directly with each other if they are annoyed with the other. DS1 is constantly calling "Mommy- he pinched me!" or even just general over-dramatic yelps of pain. I'm trying to teach him to replace that with talking directly to his brother like "Stop pinching me! That hurts!" etc.
- I try to deal with one kid's behavior kind of independent of the other kid. So I'll generalize "No pinching", and maybe remove him from the room if he continues. But I steer clear of "You pinched ds1!!" All in the spirit of not pitting them against each other any more than they already are...