Getting line weights to work with you can be tough, but it always looks fantastic when it comes out well. This one it looks like you free-handed, which I think is the easier way of getting the lines how you want, but I've noticed some of your stuff looks like it was done using the pen tool, which I'm definitely no expert on, but tried learning it when I was first getting into digital stuff. To get line weights with the pen, you just have to put the brush to whatever size you want the thickest part of the line and hit "simulate pressure" when filling the pen paths. It's then usually a good idea to stroke them again with the brush on 1px and the pressure turned off. But to me, free-handing is so much easier and less of a hassle even if sometimes ya gotta cheat a bit to get a straight line. xD
No problem~ Happy new year~!