Hey Xor! Welcome to Rescreatu! We're glad to have you. :)
My best advice for saving up TU is to buy stocks. Once you have enough TU, you should be buying/selling at the 50,000 stock limit every day. I make at least 20 mil a week this way. Good stocks to buy include ARM, BLA, BOO, FRE, and TOY. I'll usually buy at 30 TU or lower and sell at 300 TU or higher. When in doubt, you can ask the lovely people in the shoutbox for advice!
If you have any other questions, don't hesitate to ask! Zen and I will be here.