I've been making my own for quite a while now. Start off by buying smaller quantities and simple flavours. I have my trusty favourite as Apple and menthol. Nice and crisp. Only thing is to never go overboard with flavourings (especially menthol). It's easier to add a bit more to get it right than try to salvage something with flavour all over the place.

I started doing it because I wanted to slowly reduce the amount of nicotine. I love vaping, but wanted to cut down the bad stuff!
Tip number one. Don't give up. If you don't like the first batch you might like the next.
Tip two. Get a mixing app on your smartphone such as ivape for the iPhone. It takes the maths out of it. And save every mix you make. That way if you like a mix it's easy to input the percentages again and make it in bulk.
Tip three. Save every bottle you've got so far. You'll be grateful to have a selection of bottles to use. I've got to the stage where I'll batch make a bunch of liquid maybe once a month. If you can do it big with favourite flavours it'll take the stress out of it and you'll find you make smaller different flavour juices because you want to rather than have to.