As others have said, definitely check for chain stretch and check the cassette for wear. As Zyante says, chain line is critical so it’s generally best to be on the biggest ring when shifting to the smallest cog. As to derailleur alignment, I still do it the old-fashioned way. Put the bike on a stand and pedal the cranks with one hand while you shift the rear derailleur with the other hand. Then adjust the shifter cable tension slightly and do it again, watching and listening for how quickly and smoothly it shifts to the next cog. If it’s worse, adjust the shifter cable tension the other direction. Repeat ad nauseam, although it shouldn’t take long to find the sweet spot. I prefer to do this between the two cogs I use the most.