Not hard to do at all, althout you do jeed to measure accurately and there's a learning curve like everything else. E-
juice has 4 main components: propylene glycol or PG, vegetable glycerin or VG, nicotine (if you use it) in some kind of carrier fluid, usually PG, VG or a mixture; and flavorings in a similar carrier, and also if you use it. PG does
throat hit, provides miscability, and is an excellent carrier of flavorings. It is normally used in 20-60% ratios. VG provides vapor in white clouds, is easy on the throat, and has a slightly sweet flavor of its own. VG is hard to mix, hard to wick and does not carry flavor all that well. It comprises 40-80% of most e-juices. Nicotine is self explanatory, and flavors have to be worked out like spices in a recipe. The important decisions you have to make are PG/VG ratio to give you the balance of throat hit and cloud you like, plus nicotine level. After that, it's mostly trial and error to get the right combination of flavorings to suit your taste, plus re balancing the PG/VG ratio since most flavors come in a PG base. The rest of it is measuring and mixing. You'll bfind a lot more info over in the DIY section.