The serve signals the start of a rally so its standing as a key game situation is self-evident. It follows that for beginner and intermediate players the most pressing and basic tactical goal is to get the serve 'in' li.e. to start the point). As these players develop, so too should their use of the serve: they should increasingly think of this game situation as an opportunity to place their opponents under immediate pressure.
Further, as important as first serves are, it is often the effectiveness of beginner and intermediate players' second deliveries that is more critical. In fact, it is not uncommon for the same to be said of all players serves. So, even though beginners may look to develop powerful first serves to force their opponents into error, second serves should, above all, be consistent and 'IN'!