FWIW, as much as my siblings and I (3 girls and 1 boy) irritated and harrassed each other as kids, we are all adults now and have reasonably close and loving relationships with each other, and enjoy each other's company.
Nothing is guaranteed in life, but there are things my parents did, and things I want to do with my kids, that give a better chance for good sibling relationships.
Primarily, understanding that annoying/picking at each other is going to happen, and is normal....parents can do a great deal of good by not allowing that to become ongoing bullying and by helping children learn how to work out differences peacefully rather than fighting.
My boys argue and tussle a lot, but they are also each other's best friends and love each other very much. My rules are very basic: We do not abuse each other in this family. End of story.
Deliberate injury of a sibling is absolutely unacceptable, ever. Punishable offense.
Injury through thoughtlessness or carelessness also gets consequences, though not as dire and the injured one is encouraged to forgive and be understanding that it was a mistake and no something to hold grudges over.
Denigration and verbal bullying is always unacceptable. The minute I hear a conversation going in that direction, their life stops while we deal with what is going on and find a better way to manage whatever it is that is upsetting someone and prompting those words.
On the other side of that, if I see a child starting to want to play the victim/martyr role, and cultivating bitterness, I also deal with that attitude privately with the child.
Other than that, I spend a lot of time talking my children up to each other, pointing out their good sides, the kind things they've done, how much fun they are, and encourage my kids to speak about each other in the same way, and to think about how wonderful it is to have their brothers. We had a neat conversation last year, about what life would be like without their brothers. My youngest was 4 at the time, and had been struggling to find his place with his brothers, and sometimes being overly agressive with them, but he actually cried a little at the thought of being alone, without his brothers. It was a very sweet moment, and we have those, once in a while. :)