@dragoscar Firstly, I don't think I'm very good at sideboarding. It's just not a strength, and I think it's one of the more difficult skills in general. That said, here's what I see working for me and other people.
Firstly, make a definite determination about what you think your metagame is/will be. Think about it mathematically. How much of the field do you think will be what archetype, and also what decks are you good against and what decks are you bad against to begin with? I am sure that this is what really good players are doing... estimating the odds of seeing each type of deck and the odds of beating each of those deck with main board cards, so that they know where to focus their efforts in the sideboard. This is what I try to do... I'm not good at it, but I try.
If that's good and you're comfortable, a third thing you can think about is how much the potential hate cards will damage the opposing deck. (For example, when I board against dredge I try to have a lot of bullets, since it usually takes multiple hate cards to really kill off that deck... against Shops, I run fewer hate cards, but ones that are in my opinion, crushing. I tend to run decks with high land counts that can support Energy Flux. (Not saying this is good or bad... I just tend to run a lot of land and so I end up running this card.) Against most Shops decks, and again, Shops players are welcome to dispute this, landing Energy Flux is just game over. So it's not like you need a lot more. So the math on that would look like, every time I hit dredge with a hate card, it might improve my chances to win by 10% or so. Every time I hit Shops with a Flux, my chances to win go up dramatically, maybe by 40% or something. I shouldn't need to draw multiples of that card. Landing one should be plenty.
Another nice tactic, and my wife uses this to good effect, you are allowed to bring sideboard notes. My wife has a little book she carries with her to tourneys, with all her sideboard configurations against various decks. Example, if she see's an Oath deck, she looks it up for game 2 and makes an automatic board switch that she's already practiced and has written in her book.
Lastly, I really like cards that are good in multiple matchups. Cards like Containment Priest and Grafdigger's Cage are clearly awesome, because it hits Oath, Dredge, and anything running Tinker. Ingot Chewer is good against Shops type things, but has a splash effect against Dredge by clearing your opponent's Bridges. And so on.
It all depends on what the meta looks like and what decks you think you need extra help against given your initial matchup, and then how much help you think you need.