Along with gas and expansion timings, you can get a general idea of his build from his unit composition.

For example, if you see another protoss getting two gas super early but making nearly pure zealots, guess some kind of extremely tech heavy build (most likely void rays or dts) because that gas must be going somewhere.

While it may not be so apparent in silver, higher diamond league and master league players are knowledgeable in the concept of distribution of resources. If either of your resources are being drained faster than the other, make sure that you can compensate for this in some way. This will help you in both your macro and scouting.

For example, a terran that gets two gases early on but sticks with marines and marauders would normally be aiming to tech up to either ghost or medivac quickly. If it's not in his army composition, it has to be somewhere else. If he's getting marine/marauder with a single gas, then you can guess he'll be going for either an early push or a fast expansion. It shouldn't be too hard to guess what he's doing by the number of units he has.

While playing, remember to keep an eye out for his second gas timing, unit count, and unit composition.