How to Buy Minimum/Small Amounts of Stock

Review your current checking, savings and other bank accounts. Compare this to outstanding debt that you owe and determine the amount of money that have readily available to invest in the stock market. This is an important first step because the amount you can invest will help determine where and what type of stock trading account you can open.
Research online stock trading accounts to determine which one will suit your own needs best. Pay attention to minimum opening deposits that they require and note trading fees and also if there are minimum per transaction requirements. For example, some online trading firms require a minimum amount to open an account, while others do not. There is also a wide range in terms of what each firm charges per transaction or trade. Make a note of all of the options and decide which one suits your needs best.
Open an online trading account. Online trading accounts have much lower fees in comparison to using a traditional stockbroker, which is more in line with small and minimal stock purchases. As of July 2010, online trading accounts had fees for buying and selling stock as low as $4 per transaction. Some online trading accounts offer the first trades free which is also a good incentive for an investor only looking to buy a minimal amount of stock.
Treat your small stock investment account the same as you would any other investment. Review your account balances at least once per month to make sure that the money you have spent on stocks is providing you with a return on your money that you are comfortable with.
Continue to buy and sell stock in small amounts and fund your account with additional money when you are able to. Even those buying small amounts of stock occasionally can build a nice-sized portfolio over time.

How to Buy Common Stock

Open a brokerage account, either online (cheapest) or with a discount or full-service broker. Experienced traders can save money online while novices will probably benefit from the advice of a broker, at least for a while. Deposit funds in the account and wait for the money to clear. Although some firms have no account minimums, many will require at least an initial deposit of $1000 to $2500.
Pick the stock you want to buy and pay close attention to its price and the direction that it's trending in. If the price is falling quickly and you want to buy, then you can place a market order, which means that the pit specialist will give you the specified number of shares at the prevailing market price. But if the price is rising, you will be wise to set a limit on the price. For example, if the stock price is currently $47 and rising, then you might place a limit order at $50 per share so that you don't end up buying in at the top.
Get the trade you want by specifying 'All or None' or 'Fill or Kill' on your order. If the trader cannot get you your entire order at your specified price, then the trade will not go through. Fill or Kill orders have the same condition, but they must be done either immediately or not at all. AON orders can be left standing.
Regardless of whether you use a full-service broker or place your trades online, you must supply the same information. For example, if you buy 500 shares of a stock at $50 FOK, you would either simply tell your broker that over the phone or type that order into the computer system. Most online trading platforms would require you to enter in the numerical data, and then click on a choice specifying such things as AON or FOK.
Use the tools on your brokerage website to follow and chart the movements of your stock. Even most full-service brokers offer web tools and market research and commentary for their investors. If you cannot get hold of your broker when you need to place a trade, call the firm's trading desk and they will be able to help you.