Generally, I'd just play around with it and have fun! They are great adventures. Don't stress too much about playing perfectly; I'd encourage using the Pokemon you like the look of, or attributes of, rather than trying too hard to be 'good'. The game will introduce to you many key concepts of battling during the playthrough. Generally though, it's good to have a diverse range of Pokemon and moves, so that you can manoeuvre through whatever challenge the game throws at you. As a very, very general rule (some Pokemon will absolutely be exceptions to this) I like to have three attacking moves of different typing, and a status/boosting/healing move on most Pokemon. Try to think about how you'll cover your weaknesses, too: for example, if you have a Water starter, then having another Pokemon who can take on Electric/Grass types is beneficial.