Some good examples have been mentioned (first thing that came to mind for me was Castlevania games
) although often the mechanics are just jump/attack which are easily figured out, or you're meant to die anyway or the boss is relatively easy, which has also been mentioned.
If you think that it would not be obvious enough that the boss's missiles must be used to break tiles, you could have a scripted event / mini cut-scene where your character dodges its first missile, which then breaks one of these tiles.
If you don't want it to be spelled out like that, you could make it obvious that those tiles are breakable could also guide the player's judgement. An example of this is the cracked walls in Zelda games which you can then bomb.
You could also try making a full wall of breakable tiles, such that it becomes inevitable that one of the missiles will hit the wall (if only by chance the first time), and then once the player progresses past that wall the breakable tiles can be more strategically placed.
As for the sweet spots, do you mean spots on the boss, or spots where the player can shoot from? Either way, if you're worried that the player won't figure it out, just make it more apparent from the design, eg a different coloured tile for where the player should stand, or make the weak spots of the boss more obvious. Sometimes it's criticised that having weak spots be glaringly obvious can take away some of the challenge of bosses (an example of this is again, Zelda games) but at the end of the day it's better than players being clueless and frustrated in the earliest stages of the game.
But as Rivon rightly pointed out, if you're still unsure then the best way is to get people to play it! Seeing as you're worried about less experienced gamers figuring it all out, try and get some people like that to try it out, and then if they struggle ask why, or what would make it a bit easier to understand what they're doing.
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