より, ほうが, and いちばん
Track the reference point and the item being compared. Keep both items in view so that affirmative and negative patterns do not reverse the comparison in your interpretation.
The reference point before より
電車はバスより速いです。 means 'The train is faster than the bus.' バス before より is the reference point; 電車 is described as faster. Switching the nouns changes the direction of the comparison.
AよりBのほうが〜 expresses a comparison too. バスより電車のほうが速いです。 describes the same relationship, highlighting 電車 with のほうが. Check that both sentences preserve the same comparison.
Ask which of two
電車とバスと、どちらが速いですか。 asks which of the two is faster. A possible answer is 電車のほうが速いです. Identify the pair being compared from the question or preceding context.
バスは電車ほど速くないです。 means 'The bus is not as fast as the train.' Read ほど together with the negative as 'not as ... as' so that you preserve the comparison's direction.
The highest degree within a set
この三つの中で、これがいちばん安いです。 means 'Of these three, this one is the cheapest.' When using いちばん, make the comparison set clear.
Criteria such as speed and price depend on the situation. The exercise is not teaching that trains are always faster; it is teaching you to identify which item the particular sentence describes as faster.
Check: If 高い refers to price, which is more expensive in AはBほど高くないです。?
Show the answer and why
B is more expensive in this comparison. The sentence says that A is not as expensive as B.