There are a few types of soil pH test's you can do...
The 2:1 (slurry): Get some distilled water, needs to be distilled. I keep a gallon around for clones and the occasional 2:1 test. Get a clean cup of some sort, Nothing to large because you want to get your pH meter in it and reading accurately. Take a tablespoon of media from the container of your choice, I like to do a couple if its in flower and each pot monthly in my mother room. Now apply 30ml (2 tablespoons) of DISTILLED WATER (If it isn't 7 and 0 EC it won't work right). Mix it let it sit for a few minutes, then dip in your meter. Get your pH and EC. Then refer to the set points for your growing media etc.
2:1's are good for checking to see if there is something off in your media, for example you added to much guano to the mix so its way to hot. The 2:1 will help demonstrate that. They take time and are kind of inefficient. Really the recommended thing for people in organic mediums who have to monitor decomp in there media.
Run-off: This is what your talking about, Its a great way to measure the amount of available nutrients in an organic medium. Its also really good for seeing if your plants are using the fertilizers your applying when you water.
Sauce pan under the plant works ehh, I would recommend putting a cup under one of your drains and allowing it to fill up. In a professional setting we generally have a little rig that fills up and is checked daily. If your EC rises above the intake EC you know your plants arn't using the salts and there is something wrong. Could be pH, disease etc.
^^ Great warning sign, it can also help you prevent burn. Even though its generally to late at this point.
Water going in (I cant think of the actual name I learned for this, but hey. Its gonna work.): The water you going to give your plants, test it before you water them. Its just that simple.
You better know what your giving to your plants. Test the water going in, Fix it if it isnt right. H3P04 (Phosphoric acid) is really cheap, and can be ordered in bulk at high concentrations(95%-97%)! Dilute it if your EC is to high for the stage of growth your in.