Earnings season kicks off this week with Alcoa's report on Tuesday. In the banking sector, Wells Fargo & Co. (NYSE:WFC) will set the tone when it reports this Friday, July 11 before the opening bell.

Wells Fargo has been one of the best performers in the sector, and is the first of the "big four" U.S. banks to see its share price and dividend payments rise higher than they ever were before the financial crisis.

More important than the quarterly earnings numbers themselves is the answer to the question: Will Wells Fargo keep up its excellent growth? Here are a couple of things to keep an eye on that all have to do with a common theme in Wells Fargo's growth strategy: becoming its customers' only bank.

Growth in the credit card business
Wells Fargo has stated its goal to put one of their credit cards in the wallet of every one of its banking customers. Currently, the penetration rate in Wells' retail banking households is 38%, which has grown considerably in recent years, but the company has made it clear they want more.

The reason it is very important to pay attention to the company's data and comments related to the credit card business during this earnings report is to see how Wells' amplified efforts in this department have paid off, specifically the partnership with American Express (NYSE:AXP).

The two new Amex-branded cards, the Propel 365 and Propel World, weren't made available until May 6, so the second quarter earnings won't have the benefit of a full three months' worth of application and spending activity. However, we should at least get some idea of how it's working out.

Things to pay special attention to are payment volumes, which were actually down 7% year-over-year in the first quarter. American Express customers are known for their higher-than-average spending, so an increase in this category would be welcome news.

More brokerage customers
Since the acquisition of Wachovia, Wells Fargo's Wealth, Brokerage, and Retirement (WBR) business has grown tremendously. In fact, when the company reported its first quarter earnings, retail brokerage assets grew 19% year-over-year and total client assets rose by 8%.

The reason this business is so important to Wells Fargo is not just for the obvious things that come with growing a brokerage business such as higher commissions and fee income. The brokerage and wealth management business is so important because it brings some of Wells Fargo's best customers.

The average household that banks with Wells Fargo has a little more than six products with the bank, including checking and savings accounts, credit cards, loans, and other types. That's pretty impressive, but the average customer in Wells' WBR division has more than 10 different products, and the number keeps rising.

The "cross-sell" number is the one to watch here. During the first quarter, the average WBR household had 10.42 products with Wells Fargo, up from 10.33 in the year before.

So, a higher cross-sell number and growing number of brokerage customers can produce a "ripple effect" of new business throughout the entire company, and it is very important to Wells Fargo's sustained growth.

Are things going gr-eight?
This ties in to the other points of the article. A good part of Wells Fargo's growth strategy comes from their existing customers and selling them more products. In another words, Wells Fargo wants to be its customers' only bank.

The bank calls this strategy "Going for Gr-Eight" to signify the goal of getting each of its banking households to sign up for eight different products, a target which the company has been inching toward for the past several years.

Wells Fargo's overall cross-selling rate is currently 6.17 products per customer (household), up from 6.1 a year ago, and the credit card business and WBR division could provide this figure with another nice boost this quarter.

We'll just have to wait and see on Friday.