Let's be real. There are about .00002% of people who have perfect brows, and if you're one of them, I'm super jealous. For the rest of us, brows are an ongoing learning process. Whether you're young and just starting with shaping brows or a brow black belt, these are my best tips I've learned through the years.
1) Start with a wax. If it's your first time playing with brows, or you just can't seem to get a good shape, go see a professional first. Waxing isn't too expensive or painful for brows, and a super quick 15 minutes. From then on, you have a shape you can go off of, and a fresh slate. Plus, it's a lot easier for a professional to see what shape would suit your face, and doing exactly what you want.
2) Good tweezers are a good investment. Tweezers that are with a sharp edge, easy to handle, and stainless steel will be the easiest to use. Drugstore tweezers are less sharp, making it harder to tweeze the specific hair, and easier to make a mistake, plus they don't last as long. I suggest Tweezerman tweezers, because they are super accurate, good for beginner and advanced alike, and last for years (I've had mine for over 7).
3) If in doubt, don't pluck. Over-plucking can ruin brows for a long time. Though you may be plucking pretty often, longer hairs on the brow-bone take much longer to grow back. If there is truly a hair you can't decide over, don't pluck it. It will barely be noticeable enough to make a difference too.
4) Use the buddy system. Plucking brows to a certain shape is very difficult on yourself. I will always have my mom look at my brows from a semi-distance to tell me exactly where the tweezers need to go. It's a lot easier for someone else to look at the proportions, and it helps prevent over plucking.
5) Look up close and at a distance. Similar to number 4, looking at your brows from a distance gives a general idea of where you need to pluck. Looking up close gives you specific hairs that need to go. Alternating between views will give you the best chance to get a good shape, because it allows you to see individual hairs that make up your brow shape.
6) The classic "brows are sisters not twins." If you do your brows, you've probably heard this statement. But it still is very true. Eyebrows will never be exactly the same, just like other proportions on your body sometimes aren't the same. Knowing this tidbit can help prevent over plucking, because the shape of each brow doesn't have to be a complete copy. With a bit of brushing and penciling in, your brows will be very sister like, and very beautiful.