What servants is good to i focus?

First off, you have Waver which should be who you should focus on first as he will serve as a great support for your team(like to this day in Japan he is still a solid support). Hassan is another solid choice in terms of support as he sends crit stars out like few others really bringing out the potential in your team.

For your offense, depending on where you are, Siegfried can be a good asset in Orleans for the dragons, though Sasaki is another solid choice and most people would choose him over Siegfried(I personally like and use both when battling dragons but hey that’s me) there is also no such thing as a bad archer so Billy and Kid Gil are also great. Elizabeth was actually my first servant from the tutorial summon so it’s only fair I mention her too. Her np is great at leveling down the field and defeating everything in sight(especially with that Waver who will only serve to increase her damage output).

Ultimately though, use who you want to play with. In the beginning it isn’t as important to really set up your team to serve a specific purpose so really feel free to experiment with different builds surrounding around bringing the full potential out of your favorites and don’t neglect to consider what craft essences to use on who(choose to either bring out a strength or to fix a weakness). This website is a great resource in guiding you in the right direction for builds and can go in more depth at the different types of team comps.

Hope you found this helpful, my friend code is 529,751,840 if you want to see what Siegfried and other servants are capable of. I have a Cu Alter and a Brynhild at the moment too in terms of five stars.

Waver yes. S+ tier support skills.
Camilla is amazing at killing rider bosses and female servants.
Elizabeth is a solid all rounder but nothing special. Of course you'll be using her for any archer heavy quests.
Seig is great against dragons and dragon type servants but his specialty is a bit niche so he can probably wait until your other gold servants are leveled.

Of your other servants you should try to cover the classes you don't have golds for. I recommend Ushiwakamaru for Rider, Billy the Kidd for Archer and Kiyohime for Berserker. You'll also want an offensive caster since waver is mostly support, so Medea is a good choice for assassin boss killer with her NP spamming potential. You'll also want a critical star generator, Cursed Arm Hassan is your go to there.

Oh and don't neglect Mash she is absolutely irreplaceable as a defensive support and as the only 0 point cost servant in the game.

Once you have those leveled you'll be well on your way to having a solid roster.