Accounts Receivable - AR is when the company has made the sale but has yet to collect the money. Sales drive accounts receivable, therefore when sales are growing you would expect a similar growth in accounts receivable. A problem starts when AR is increasing at a faster rate than sales. This is a highly illegal practice that almost always catches up with the company. Inventory - this ties in closely with accounts receivable.
Inventory is finished items available for sale.
High inventory is bad for several reasons. First, because there is a cost associated with storing the extra inventory, increases in inventory causes higher storage costs. Secondly, increasing inventory can mean the company is producing more than it can sell and some of these extra items may never get sold. Similar to AR, you would expect inventory to increase at a similar rate as sales, as sales increase the company must produce more to prepare for the increase in sales. Gross profit margins indicate what the company's pricing policy is and what the true markup margins are.