Sales accounts are credit accounts. So when you want to increase the amount of sales you have made, you make the entry as a credit entry. You receive a check and put it in your account debit cash. The sale, if it is an item you have on hand and give to the buyer, you enter as an immediate sale. Credit sales the same amount that you debited cash.
However, if you have just signed a contract, and have not actually done any work on that project this month, you have not yet earned that sale. You're just holding the person's money for them, keeping it safe. Since it is not yet truly a sale, it is a customer deposit. The entry will be debit to cash and a credit to customer deposit, which is a liability account (you would have to refund the money if you don't do the job).
If you have a lot of contracts going at any one time, your job will be easier if you give each job its own number in customer deposits so you can easily keep track of how much has been turned into sales, and how much remains to be earned.
Customer deposits turn into cash as you earn them through the purchase of materials or labor performed. You will need to evaluate each month what part of each job is done.
