First, let's discuss what a pool is. A pool is basically a third party service that combines smaller miners together. Mining SOLO is almost impossible unless you have multiple warehouses full of the latest miners. So we need a POOL to actually be able to solve blocks and get paid.
Choose a pool can be tricky, each one has it's own fee, each pool support different coins and so on. Find out what your miner can mine, and what is the best coin to mine at the time. Nicehash will do it for you if you choose Nicehash. Another factor is the Pool Fee. Nicehash has the highest fee but also it's very convenient. For small scale, maybe 5% is worth it. Once you grow to large scale mining operation, every penny counts, and each percentage you give away to your pool could be hundreds of dollars per month. In that case, I would recommend to choose the most popular - lowest fee pool you can find. Once you set it up, there is not much else you need to do - just make sure your machine is running smoothly.
Make sure to connect your miner to a pool URL that is the closest to you. For example, I live in the West Side of United States, so if I use ethermine pool, I would pick us2.ethermine.org as my URL for mining. If you live in Europe, use eu1.ethermine.org. This will increase efficiently and latency and give you better mining results. Nicehash has an option to change this in the settings as well.
NiceHash 5% (ethash Ethereum Pool and pretty much all coins and algorithms)
NiceHash has the highest pool fees out of everybody - but it offers easy to use software with remote control features and monitoring system. I personally use NiceHash due to the ease of use and remote access. From anywhere you can turn on, turn off and even change clock speeds on each GPU you have in your rig. Another bonus is no transaction fees when you transfer your profits from NiceHash to Coinbase. NiceHash takes 5% fee for using their services.
ethermine.org PPLNS (1%) ETH / ZEC / ETC / RVN
ethermine is the largest pool for mining Ethereum. They also support other coins to mine. You will need to download one of the supported Ethereum miners like T-Rex, GMiner, bminer, lolMiner, and, Phoenix Miner. They only take 1% fee for using their pool. They only change 1% fee.
sparkpool.com PPS+ (1%) ETH / CKB / BEAM
sparkpool.com is another large mining pool that is based in China, they have their own app that you can see live how your miner is doing. They only charge 1% pool fee.
If you use a pool but you notice things like inaccurate hash rates reporting, very high payout minimum, or technical issues, don't be afraid to choose a different one. It's very easy to switch!
If you grow big enough to mine SOLO - WOW good for you. You will still be charged a fee but it might be smaller compared to shared pool. Pay attention to not choose a mining plan or a pool that will take the transaction fees out of your profit - this can be allot of crypto that will go to someone else's hands.