Teams treat cloud cost as something to fix after the fact, with a dashboard and a quarterly panic. But most of the bill is decided at design time, long before the first invoice.
Right-size from the start. Default instance choices are almost always too big. Measure, then provision — and let autoscaling handle the peaks instead of paying for them around the clock.
Mind the data gravity. Egress and cross-region traffic quietly dominate many bills. Architect so data stays close to where it's used.
Make cost visible to engineers. When the people making architectural decisions can see the price of those decisions, the bill takes care of itself.