I do a few muscle memory warmups using my modified spray. If you want to try them, look up 'Wandeag muscle memory,' first link on Google. Basically, I took it and edited the spray to get rid of the URL (so I can use it on the servers), and to include my name and rank. After doing that, I usually do Crackhouse, get around 100 kills, and then move on to our pubs or scrims if I get invited to any.
Due to the muscle memory work and the warming up, I've seen my average scrim KDR go up to around 3-4 from <1. I would highly suggest using it.
Additionally, for added warmup, I sometimes run through popular scrim maps and watch my crosshair positioning, making sure to keep it at head level and keep it aimed at where I think my enemies will be based on the map. It definitely helps you stay alive when your crosshair is on your enemy the second you see them.