Account Value is the sum aggregate of all the cash you have in your account, plus all Equities or Assets that you have in your account. With options, it is the sum of all option values across Long and Short Positions, plus the cash in your account. Any Margin Requirements or Option Requirements will not be added to the Account Value. So basically, Account Value can be summarized as Cash plus Equity minus Requirements.
The monthly changes in Account Value determines the Trading Plan. If you are looking for 3-5% monthly return on your equity, you have to calculate the Return on Capital for each given trade and keep an eye on the Account Value as it changes every week. As soon as you reach your target for the months, you have to be more defensive and preserve your Account Value. When the next month starts, you can take more risks and follow an aggressive Options Strategy.
Always avoid negative cash caused due to interest payments and avoid buying on Margin. And remember that opening or closing a stock position within 60 days can result in tax consequences. Keep this in mind when determining which trades to close.