Figure out what kind of attack you are going to use. Ask for Clan Castle troops that will help with your attack plan. You may not get them, but most of the time you will. Donate also, but check to see if the one asking is higher levels than you. Your lower level donations won’t help very much, because the defenses they will be going up against will take them out very quickly. Unless it has been a while since they requested and no one has donated, then any will be better than none.
With the number of wars we have done, we do get a +1 level upgrade on donated troops, so remember that.   If they have level 3 giants and you have level 2 or higher giants then donate if you can. Your everyday attacks you may not want to always be asking, but definitely ask for your war attacks. If nothing specific is asked for then don’t worry about the levels, and donate if you can, assume that they just want extra troops for the attack. Cardinal doesn’t have unlimited Dark Elixir so you need to be a Townhall 8 with maxed 7 defenses before he will donate Bowlers. Mostly he wants to only donate them for war, but some practicing will need to be done. Witches aren’t that useful so nothing is set on them. He has miners now and they are regular elixar so anyone can have them. Personally though I think Hogs are better for TH7 and below.