The way NUS does module selection is different from how we do it at SUTD, hence the process was a bit overwhelming at first. For exchange students, we only have 2(?) chances to apply for modules, one during applications and the other during the ‘submit module request’ round (which I believe aligns with Round 3 of ModReg for NUS students). The module selection at NUS is not done by first-come-first-serve, but rather through ranking. This meant that it is important to correctly prioritise modules and rank them accordingly. There are also vacancy reports available for you to gauge your chances in getting modules you bid for. I personally used the number of vacancies to rank the modules during module selection. The last resort would be to appeal for the modules, which I did for 2 of my modules.
Some advice for module bidding would be to check if module is offered to Non-Graduating students and also to make use of NUSMods to plan your timetable. Surprisingly, most lessons end 30 minutes before the actual end time (i.e a 2 hour lesson is usually about 1.5 hour), so you do not need to worry about travelling from one venue to another between back-to-back classes. I unfortunately made the mistake of not putting my classes back-to-back to compact my lessons, and hence ended up with very long breaks on some days. Overall, module bidding did seem quite daunting at first, but it can be done with proper planning.