If there is one tool that has elevated my baking, I would have to say that it's a scale. For years, I virtually ignored the weights that are often included in the ingredient list. Weighing flour, sugar, and eggs felt a bit fussy to me, something that only professionals did. But the truth is, I like to have consistency in my cakes. I want to know that my cake's not going to be slightly off, just because I used a different brand of flour that day. I've also found that weighing is easier than measuring everything out. Rather than having to worry about whether my flour is properly aerated before measuring it, I do nothing more than scoop it into a bowl until the weight is exact. I've also discovered that the weight of eggs, even those in the same size category, can vary enough that it can change the outcome when a recipe calls for a large number of eggs. It doesn't have to be a huge investment, my Escali digital scale runs about $25. It's lightweight, easy to store (it's flat enough to slip into a drawer), and easy to use. If you like to bake, especially cakes, this tool is definitely for you.
Now, plenty of older recipes don't list weights, only measurements. As a point of reference, I looked to Baking Illustrated for a list of egg sizes and what their corresponding weight is assumed to be, as well as their notes on measuring flour. It's good to have information like this, so that you can finesse recipes that you make often.
Medium egg = 1.75 ounces
Large egg = 2.00 ounces
Extra-Large egg = 2.25 ounces
Jumbo egg = 2.50 ounces
If recipe reads:
1 cup all-purpose flour = about 5 ounces
1 cup cake flour = about 4 ounces
1 cup sifted all-purpose flour = about 4 ounces
1 cup sifted cake flour = about 3 ounces
1 cup all-purpose flour, sifted = about 5 ounces
1 cup cake flour, sifted = about 4 ounces