Most people who mix their own e-juice do it based on a recipe of some kind, to get as good a result as possible. Compare mixing without recipe to baking a cake without it, it could be done, but it’d be so much easier and accurate with a recipe. But it is also possible to mix wildly also.
There are countless forums and groups on Facebook where people share their recipe for their best DIY e-juice. You can also google on “Your favorite e-juice + DIY recipe”, or “Your favorite e-juice + clone recipe” and you’ll get tons of hits to choose from. For example press this link to search for Grants Custard + DIY recipe.
Other great recipe collections online is: