When learning, it is suggested to cast for mundane things you do not care about; it makes it easier to forget.
Different for every sigil I make, but I release most into the element corresponding to whatever I am going for, otherwise I burn them as a default. I do have one permanent one on the wall where I work, though, and another folded and tucked into a nook in my wallet.
Chaos sigil magick is extremely effective, especially once you tinker around a bit and find a consistent system that works for you. Experimenting is good, too. I had some excellent results from using fully charged chaos sigils as my statement of intent while working with spirit sigils as well. It seems to give them more to work with. Offerings are all well and good, but an energized focus of your exact intent really gives the work a kick start.
And it is great for starting out because all you need is a pen and paper.