One of the tips is something I do, precisely because I suck at math: pay in cash. I only carry money in amounts that my brain can reasonably handle. I don't try to do the math in my head. Physically handling the cash makes it much easier for me to track. If I want to buy something online, I hand cash to someone else for it or make a barter arrangement. For trips or other occasions that require handling larger-than-usual amounts, I subdivide it -- so much per day or per store -- and physically separate the money into those bundles. This works for me. I would rather use this simplified method than flail around with more than I can handle, making mistakes and making myself miserable.
Work with the brain you have, not the brain other people wish you had. Find a budget method that works for you.