We usually go in August. Though I’m not a big fan of either heat or crowds, I do think summer is a great time to go. Usually all the off season refurbishments are done, many of the shows run twice a night, and there is a great energy to the place! Most important advice from a heat-crowd-Scrooge: take full advantage of the early morning hours. Our family tradition is actually practicing early wake ups the week before our trip, and the kids love it, because it’s become one of our Disney prep family traditions. This way you get the big rides done before the huge crowds and the really bad heat hits. Then, when things get more intense, you can slow down to a more leisurely pace. If your hotel is close & you like staying late, consider going back for s midday nap. Most of all: hydrate, hydrate, hydrate, and have a great time!
Edited to add: Also, I find it helpful to temper expectations. We all like Stat Wars & would love to ride the new ride in Galaxy‘s Edge, but my kids know that we might not get on during our next August trip, depending on what procedures they‘ll use at the time and how lucky we‘ll be. I found that both in Disneyland and in life at large, the key to happiness is to hope and strive for the best but to also understand that disappointments and unexpected obstacles to what we would like to happen aren’t good reasons for not enjoying and not being grateful for the things that DO work out (especially those little, sudden Pixiedust surprises that we didn’t plan for and that we may miss if we focus too much on stuff that frustrates and annoys us).