1- I tend to play off the adc im playing with in solo queue. I try to adapt to their play style so if I see them trying to auto attack harass in between csing then ill try to set up a play when the enemy adc/support is a little low. One of the hardest parts about solo queue though is not knowing exactly what someone else wants to do. So if the adc goes in when I think it's a bad idea I might just walk away (trist jumping in like an idiot or something).
2- Most communication in solo queue is done with pings. If the adc or support want to fight you pretty much just spam ping and then follow that up with an engage. Aside from that, just call out where wards are for your jungler and get times on flash/summoners.
3- This one is hard in solo queue I've noticed because a lot of the times the adc is going to lose farm/experience if the support roams. It also depends on what adc it is, someone like a kogmaw will have a hard time in a 1v2 lane.