There is a simple rule which worked in nearly 100% cases about when to use TO or -ING pattern verb. The rule goes like this: “If the first verb happens before the second verb, use TO. If the second verb happens at the same time or before the first verb use the ending -ING with the second verb. For example: I want to go out. (First I want and then I will go out) She stopped smoking. (First she smoked and then she stopped.) He agreed to do it. (First he agreed and then he did it)”Simple, isn’t it? However, you have to be careful as the rule does not work for the verbs suggest, pretend and fail.