Your initial considerations in selecting your openings should be:
- The style of game you like
- A little bit of everything, a lot of somethings
Style of game is interesting and multi-faceted: Do you like to go straight for the king? Do you like an open board? Do you prefer a game rich in strategic concepts? A game where you manoeuvre to induce weaknesses before launching an explosive counter? Or a game where positional motifs dominate?
You may have a distinct preference, or more likely a combination of ideas. Based on your understanding of these you can then start selecting openings that are appropriate to your style. Perhaps line opening gambits such as the Goering or King's, a Ruy Lopez, the Sicilian for richness, the King's Indian for explosive counters, or the French for a positional game.
Whilst you will have favourites lines and common openings that you learn in greater depth, it is also important to have 'a little knowledge of everything'. For example, if you play the Ruy Lopez, I would expect you to know your favourite Lopez lines, and how you meet the Sicilian and French in some depth, but also to have a little knowledge of how you will react if your opponent chooses the Scandanavian, the Caro-Kan, the Pirc, etc. Making a little checklist can help in this regard.
An opening repertoire is a big subject which we will look at in more depth in future Improvement Tips.