How to choose a stake pool to delegate
Let me explain some of the criteria on how to choose a delegation partner.
First, check if it is a reliable pool operator. Past operational performance will be helpful. You can use this website to find out how the stake pool is operating. (Type ticker in the search window)
The next step is to check the amount of delegation.
A pool with a delegation amount between 3M and 50M seems to have a stable reward.
Stake pools between 100K and 3M have a larger element of chance, so the rewards are sometimes large and sometimes small.
But basically, the expected value of all pools converges to about 5% per year, so it is a matter of preference.
For pools below 100K, if the pool is not generating blocks, you will not be rewarded, so it is not recommended if you have less than 100K.
However, the basic idea of Cardano is decentralization. With this in mind, it is very nice to contribute to the decentralization by delegating to a smaller pool, or supporting that pool operator, although it is almost always a good idea.
Please note that stake pools with more than 64M delegates will be rewarded less. (The saturation point is set at 64M)
Finally, you can basically just leave it alone, as the rewards will be automatically re-delegated without you having to do anything, but I recommend that you periodically check the pool you are delegating to using the site mentioned earlier.
One is to see if the reward is in place.
The other is to see if they have changed their fees. Please be aware that there could be malicious fee changes.