I don't look for "opportunities" with few exceptions. I look for balance.
For example, I have any funds I expect to need for five years in cash (equivalents). So, to keep that I can't leave my portfolio alone, a year goes by and I need to replenish the cash. The next five year period I have invested in "safe" stocks (the term is misleading a bit). The next five years is in somewhat more speculative stocks (and ETFs).
After that I can afford to be somewhat more speculative, I own a good bit of Apple for example, Amazon, Google, etc. The problem is that these stocks have run up which means I should be selling to rebalance my portfolio, and I did sell some Apple, a move I now regret obviously, but whatever, I was getting way too much Apple stock, and still have too much, I'm over 10%. I wanted to stay under 4% with any single investment.
And of course I take out cash each year to pay bills etc. So, my main focus is simply allocations. I have been off my model for a while now but I still have a heavy portion of cash eq.
If you are younger, you should be more aggressive relative to how many years you have before retirement.
I wouldn't buy a single stock with a portfolio under $100 K, even half a mil you can do fine with ETFs.