Main tip right now has to be: don't sleep on any Pokemon.
You have a lot of Growlithes? Good, have evenore of them. You never know what will the new "gym rework" bring. What will be the new meta? And Arcanine is still super competitive in every Pokemon game there is.
Same with Flareon for example, top 3 attacker right now? Pillowswine awesome Dragonite counter and has gen 4 evolution. And more of the same like that.
Try to throw great throw every time and use discounta wisely.
edit: very unlikely, but maybe don't evolve Pokemon until gym rework because you never know what can happen with attack so maybe wait just one week