Basically you need something to measure your ingredients. I mix by weight using a scale that can measure down to 0.01 grams, others use syringes, or pipettes, graduated cylinders.
You will need something to mix in. I just mix in bottles.
You will need PG, VG, nicotine base, and flavors.
I suggest starting with known good recipes from here on VU or ELR. You can also find what are called "One Shots". These are recipes where all the flavors have been pre-mixed. You then add the percentage of the One Shot to your PG, VG, and nicotine.
DIY mixing doesn't need to be hard. Actually it is quite fun and you will save money in the long run. Most of the recipes I use cost less than $1 for 30ml to make.