When you start with a search campaign for the first time you can start really small with a few exact transactional keywords and see if you get some traffic and conversions with those keywords.
You could also start broader with phrase keywords and see what that does. After some weeks you can still exclude keywords or make keywords exact.
There is no one-size-fits-all strategy. Based on previous experience and specific keyword research you can of course make a guess about what works and start with that strategy.
You can also try first going broad and then small or vice versa.
