Things to do before buying a stock:

1) First thing to know is what the company does and how it makes money. (or how it plans to make money).Understand the business model.
2) Understand its competition and how it compares to them. Is it best of breed ? Is it catching up with others. Does it 
    have a rule breaking product?
3) Look at the quality of management.See how long they have been there. How much experience they have in this field (maybe from
    other places). Is the management share holder friendly. Too many options will be dilutive to earnings.
4) Look at the last few years of company performance to see if it is profitable. Are earnings and revenue growing?
    Are margins improving or not ?
5) Look at the cash Flow statement to see if there is Cash flow growth. Look at cash flow from Operations - capex.
    If cash from financing is more than cash from operations that is a negative sign. Look at change in inventories. Are they rising faster
    than sales? Could be dangerous. also look at the change in accounts receivables. Calculate Cash King Margin
    = FreeCashFlow / Annual Sales. Greater than 10% is good. More the better.
6) Look at the balance sheet to see how much cash the company has versus Long term debt. Is the debt reducing?
    If the debt is increasing, what are they doing with it . expansion ? acquisition ? What is management plan
    on reducing debt. Strong balance sheet will provide a margin of safety and cushion in bad times and such a company may be able to survive a   temporary reversal of fortunes.
7) Does the company pay a dividend? what is the yield? Has the dividend increasing last few years/ quarters?
8) Does  the company buy back stock?
9) Look at ROE, ROA, ROIC, net profit margin, gross margins. Earnings growth, revenue growth.
10) Look at income statement to see if revenues are increasing. Make sure cost of sales is not going up faster than revenue growth.
11) How are the companies products/services. Do you use them? Heard of them? Any good stories. If its a store, you can visit it to see
     how customers shop there etc.
12) Ask questions you may have to the investor relations. Most companies have a good IR dept and reply by email/phone.
13) Categorise the company (a) fast grower (b) ever green/blue chips/stalwarts (c) turnaround (d) cyclical (e) asset play (f) slow grower
14) Look at the current p/e  and compare it to its historical p/e range for last 5 years.( from moneycentral.msn.com or bigcharts.com)
15) Study a bit about the companies history. How long has it been operating.
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Things to do when you buy the stock:
1) Write down the reasons you bought the stock in brief and your expectations from the purchase. Is it a speculation or a well informed
investment. Is it a long term holding or a short term play. can you explain the business model to some one else.
2) write down the date of purchase, the price paid per share, the P/e on the date of purchase. write down the EPS as well.

Things to do for a regular stock check up:
1) Read the quarterly report to see how the company did in the quarter. Was the company profitable. did revenues/profits increase. By how much.
2) Calculate the TTM EPS.
3) In the quarterly report, check out for the regular things that you analysed before buying the stock. (i m assuming you did) such as
margins, earnings growth, options expense, cash flow, debt, cash.