Never underestimate their cleverness.
Specifically, one of my brothers has always had a knack for building things. Most of his time was spent in the garage and I never really cared to look into what he was doing. There is where I went very, very wrong. Multiple times he led me to believe that he was simply working on a small project that could be seen as non-dangerous. However, after closer examination, I found that these ”projects” were usually comprised of extremely dangerous and sometimes scary components.
Never take for granted the younger years.
Being the second oldest, I was larger than my two younger brothers for a solid fourteen years. However, after finding myself actually losing a wrestling match one day, I realized I was no longer able to pin my brothers down. This can be alarming because of the built up frustration that they never could take out on you during those years you were so much bigger than them.
Understand that they are not a girl.
Trying to make them play dress up never works and I'd pay money to see my brothers play with anything pink. Trying to grasp that they will never understand why you wear makeup or like to go shopping is tough. Family pictures are always difficult because the guys don't see the importance. However, the girls know that pictures are memories and will be looked at for years to come. This is frustrating to say the least but eventually after saying "one more" five more times, the guys finally smile just to get it over with.
Be ready for the sassy teenage years.
Oh yes. Boys have ten times the sass of a girl. My brothers are particularly good at talking under their breath. However, I can say that they could have learned the sass from their older sister... Fights over chores and who is the better wrestler seem to always turn out a win for the boys. You just can't compete with that boy sass.
Finally, realize that they love you unconditionally.
Unlike girls, boys don't care about your hair, makeup, or accessories. All they care about is if you're good to them and if you're good in the kitchen. My brothers, no matter how many fights, at the end of the day will still tell me they love me. One brother in particular would hug me three times a day if I let him.