One of the first things you can do before even planting your seed/seedling is to make sure the soil you are using is going to be the best. To check this, a PH test kit is essential.
There are many different types out there, and they all produce similar results. Check out this video to see the one I got, and how easy it is to test your soil.
PH test kit video
The test kit in the video cost roughly $18 from Bunnings and is enough to do 30 tests.