@Jack Zhuang
The more you can keep business and personal accounts separate, the better. It's easy to meddle between the two starting out, but the best thing I ever did when I started was to set up new checking and credit cards for business expenses only. This makes tax time so much easier. 12 years later though, it is still a work in progress to keep everything separate. I'm NOT an attorney or CPA, but from my understanding if you create an LLC it is also prudent to keep these expenses separate, or the LLC really does you no good as far as liability protection. This is because if something happens and you get sued, the plantiffs lawyer can have grounds to say you really aren't separate because the accounts are ran with personal expenses. I even have gone as far as opening new accounts for expenses that are personal but that are tax deductible. This also helps greatly with tax time
