I'm fairly new at investing in stocks and I see a lot about "take a little off the table". I've never seen an example of what is reasonable to take.
I had just 148 shares of a stock that did a 3/2 split so I then had 222 shares. I was up to a value of $3750, gain of $450 out of an investment of $3300 (over 13%). I sold 22 shares for $380 to take out some of that profit. I now have 200 shares with a value of $3460, cost of $3050.
Small amounts or large the trick is to think in percentages and risk comfort levels. You can't ignore taxes but they shouldn't be paramount in your mind. Generally I try to allocate (effectivly take a little off the table) when a stock has moved up enough to be a much more sizable portion of my portfolio than I had intended (these are for sales that aren't due to a fundamental shift in the company's operations). For example, I bailed on Top not to take some off the table but because I didn't like the changes made to the business relative to the valuation. (I don't want to open a discussion on that just giving an example). I tend to take more off the table in funds, so in my 403b, I was reviewing my brackets quarterly and intraquarterly would rebalance if a moved enough to be 5% or more from my original allocation. So if small international was 20% of my portfolio in late 2003 and prior to year end it was 26%, I would reallocate some of the gains into the other funds (bring my allocation back to 20%). There are entire books written on how frequently and largely one should reallocate, but all in all it comes down to how comfortable you are with risk and without that no one can answer your question very well. I started small like you but tried to limit trades to keep commissions to 1% or less of the amount traded.
I'm sure I'll learn the more I do. I don't play with much in stocks so it's not a big part of my overall fund allocation but, I still do keep an eye on it.
I've had a return of 42% (that is including trading costs) in my "playing" money since my first stock investment late last May. Still getting a feel of things and I hate watching even just a $400 gain whittle away.
I have been in the market since about 1980, and have also used the phrase, "take a little off the table".. .I think the general principle of what you are doing is correct, but each person has different levels of risk/reward. With the small amount you are talking about, I probably would have left it all on the table. I have often waited for a stock to double, then take 1/2 off the table. I did this during the internet craze of the 1990's, and I was left with a large profit when the crash came. If I bought a stock at 10, and it went to 20, then I sold half, (which paid for my original investment) and let the rest ride. . .that way you never lose your original investment. Every situation is different, because I usually have about 45-50 positions in stocks.
I usually hold stocks for a year or more to get long term capital gains. The most recent example of this was Netflix. I bought at 10, held for a year, then sold half my postion last week at 30. . .it has since gone up, but you take your chances.