I agree, Hold Tx Freq is the first step. And I move my Tx freq often using Shift-click on the waterfall to stay on a clear frequency.
As to who I respond to first:

- I reply first to the station that I "need" the most, obviously like a new DX country or a new CQ zone.
- If there are multiple DX callers then I prioritize the rarest station first, also obvious. It's uncommon, but it does happen sometimes!
- The more common situation is multiple NA/US or JA callers - I call the strongest dB station first so I can complete the QSO with the minimum number of repeats. This minimizes the chance of me causing QRM to someone else. 
- If all the callers are about the same dB strength, I will call the POTA/SOTA stations first since these guys are making extra effort for contacts.
- And then, I do give priority to LoTW stations (red text color), but that's just my preference.
Hope this helps.73, WA5MD, Tim in Dallas