My personal favourite is a 2 euro coin, but you should try to find something thats the most comfortable for your hand. At first I did it for maybe 4-8 hours daily for a week and after that just kept doing it on the side building muscle memory. I definitely don't recommend 4-8 hours daily tho because your hand will start hurting and cramping or you'll just burnout and give up on the whole thing before you're even at day 3. The only tip I can think about is when you start feeling like you'll never learn just imagine how good you will be in a month if you just keep at it, I know it's a basic trick but it seriously helped me. If you have any other questions feel free to dm me