There is a book by GMs Wahls & Mueller about 'Modern Scandinavian', 300 pages with plenty of master games where you could study the plans & ideas for both sides. If you're White and playing against a Black player who has studied this book you will have a hard time to find a reliabe & easy winning pattern for White, but there are dozens of positional & tactical motifs for both sides, which they can try to exploit.
E.g. White can often get the bishop pair, or they can sometimes go for a breakthrough in the center (d5!), or also often the players castle to opposite sides of the board and typically this gives winning chances for both players (He who can attack the opponent more quickly has good chances for a win). Sometimes it's also a good idea for White to establish a centralized knight on e5 where it has mulitple threats: (1) Attacking Black's Qa5 at a favourable moment (Nc4), (2) after chasing away Black's lightsquare bishop, which often ends up on g6, to h7 (using the h & g pawns) the e5-knight can sometimes be sacrificed on f7 (especially when White has a bishop on c4 and a Queen on e2). etc.
So there are plenty of strategical & tactical motifs for both, Black and White, and if you wanna play well against the Scandinavian you should definitely get a good book about this opening. It is not an opening where White can simply lean back and outplay Black OTB and without any greater efforts, it's actually a very solid defence and hard for White to get any realistic winning chances even with good theoretical preparation. Except maybe on 'our' amateurish level of play, where usually the blunder factor is more decisive than any positional idea.
Basically what you need to know for White is at least one good variation, and there are quite a few of them.
Typically what I try is to somehow get Black's lightsquare bishop with my knight (as soon as it appears on g4 or f5) and then hope to open up the position to have some advantage with my bishop pair. I must admit -> on our amateurish level of play this is incredibly hard to do, but my point is that if I never try to exploit this kind of a theoretical advantage then I'll never learn how to do it.
Certainly there are some more aggressive/tactical ways for White to play than 'only' on the longterm idea of the two bishops, but they have the drawback of most tactical variations: Typically they all are very well analyzed, and playing them demands you to know a lot of theory, and hence learning them is just too time-consuming for an amateur with a fulltime job like me.
So choosing variations with long-term positional ideas, where I'm not immediately punished if I mess up the move order, seem to work better for me:)
However, if you're very ambitious, still young and still have a lot of time to learn openings then consider reading books about the openings you wanna play or those you're going to face, preferably books which don't only list hundreds of variations without any useful comments, but preferably books which contain many master games and lots of comments of a master about the strategical ideas behind the moves.
Such that in case that your opponent does play something else you have an easier time to find the pros and cons of his 'novelty' (on our amateurish level of play often the same thing as a 'blunder') OTB.
greetings
Just to make things clear, this game isn't mine. I'm trying to understand some of the possibilities as white in the main line Scandinavian, and will do my best to analyze some games from the chessgames.com database (and perhaps others as well), in hopes of highlighting any winning patterns. If you spot any analytical blunders (i.e. explanations for what I claim to be blunders), please, please point them out! If you spot any interesting combinations I missed, I'd like to know about those, too.
Here's one analysis to start things off:
Game 2: