Former office global here. At lower ranks, office is more balanced, but as you go up in skill, it gets more and more t-sided.
T side setup is very simple. 2 Ts in spawn (do not sit in long or side hall). 2Ts in paper. 1T in connector (alternatively you can have a floater switching between paper and conference room to watch connector and long). There's only two choke points to cover. Imagine being able to cover both bomb sites at the same time; connector guy can shift his focus in under a second. Do not rush as a T unless you are playing for fun, and don't push out farther than you have to.
Communication is key here is paper gets smoked off or tspawn gets breach, they need to communicate that.
If the CTs get a hostage, sitting at fountain is the prime spot to cover because it's impossible to get juked (you can cover long hall and main hall at the same time). If you retreat to the rescue area, it's easy to get juked.
I almost never would save as a T because sawed off is actually really good on this map, and you have such an advantage that sawed-offs and pistols still have an advantage over a full CT buy.
CT side is more complicated, and it's extremely hard to play with a group of randoms. I went from solo-q hard stuck at DMG for months, and after I started playing with a regular group, I literally got global in a few weeks.
Hostage locations are extremely important. If the hostages are in long hall and paper, suddenly the map becomes much more balanced. Long hall hostage in particular makes things way easier because long/side are harder to hold, and CTs can just smoke off T spawn.
Coordinating buys is important, and shotguns/pistols can be viable for paper whereas long hall guys are going to need rifles.
One basic strategy is that all at the same time, one group needs to put pressure on long hall/side hall/tspawn, and the other side puts pressure on paper/elbow. This means if you get an opening kill, you might be able to flank some Ts.
Learning pop flash lineups is extremely helpful, and this is where playing with at least 1 person you know will help to take advantage. Pop flashes are basically a requirement at global. There are some smoke lineups as well, so you can smoke off something in order to push forward without peeking. Also since we are talking tight corridors, you can actually learn some great wallbangs.
If someone gets a hostage in T spawn, the paper person needs to retreat and cover that choke point. It's basically a free kill. If someone gets a paper/projector hostage, the tspawn person needs to sit connector.