How you categorize and prioritize your relationships is important. I believe quality over quantity applies to relationships as much as anything else.
I'd always prefer a few close friends over a lot of "sort of" friends and acquaintances. But that's me. You need to decide for yourself what you want.
Either way, though, investing in the relationships we care about is what's important. But my quality-over-quantity principle does help here because there's less investment overhead with a smaller group of relationships.
But this is also another hidden land mine because family size varies drastically. Maybe you have double-digit siblings or cousins, or a lot of extended family.
But this is the best place to start. Focus on your immediate family and the closest relationships within your family. Keep track of birthdays, when you last talked to everyone, gift ideas, and little nuggets of information.
I'm notoriously bad at keeping up with my parents, sister, and brother. I'm great with my wife, son, and step-daughter because they are always right in front of me. But the rest of my immediate family isn't as much. So I have to make a concerted effort to track these things and reach out regularly.
Don't invest in relationships that do not give anything back. If you're the only one making an effort, it's probably time to call it a day on that relationship — or at least until they reciprocate. The exception to that rule is children (and maybe your significant other). These are the types of relationships you should over-invest in, and work through the times when it feels one-sided.
You should nurture relationships with people who make you laugh, smile, and feel like your best self. They should know you through and through, and you should feel comfortable in their presence. Don't waste time on drama. I hate it, and I've shed as much of it as I can.
We all have had those friends — and maybe still do — that just can't keep away from drama. They almost yearn for it. It's as if their very being and existence would shrivel up and die without the presence of effervescent drama. They crave it, and they want you to crave it, too.
Live a life free of it. Enjoy the healthy conflict that conditions growth. But don't confuse that with soul-sucking, narcissistic drama. It doesn't give. It only knows how to take.
Focus on the good. Cherish your best relationships. Enjoy your life.