Xiàng(向) and duì(對) both could serve as a preposition or a verb. When used as a proposition, xiàng(向) indicates that an action is performed towards a reference point, which can be a specific direction or a person. When duì(對) is used as a preposition, it means to or towards an object or target. When conveying the meaning of towards or to, the specific similarities and differences in usage between these two words are listed as following:
xiàng(向)/duì(對)+ person+ action verb
tā xiàng /duì wǒ huī shǒu.
He waved to me.
duì(對)+ something/person+ adjective / state verbs
lǎo bǎn duì nǐ hěn shī wàng.
The boss is very disappointed with you.
wǒ duì yīng yǔ hěn gǎn xìng qù.
I am very interested in English.
xiàng(向)+direction/ noun(pronoun) represents an explicit direction of the activity + verb
nǐ xiàng dōng zǒu yī bǎi mǐ jiù dào shū diàn le.
You will arrive at the bookstore after walking a hundred meters eastward.
tā xiàng wǒ men zǒu lái.
He comes up to us.
Xiàng(向) also can mean “from” according to the context, but duì(對) doesn’t have this kind of usage.
tā xiàng wǒ jiè le yī bǎi qián.
He borrowed a hundred money from me.
wǒ men yīng gāi xiàng tā xué xí.
We should learn from him.