When do we need
1) main verb + noun + verb(ing) &

2) main verb + noun + to + verb ?
It depends on the verbs:We have different verbs that are followed by "to" and sometimes "ING".

e.g:After verbs like (feel/smell/see/hea,perceive,notice,observe.../object+ ing/ bare infinitive

1-I heard someone sing(complete action)/singing (action in progress)

but after a verb like KEEP we use just(gerund): sorry for keeping you waiting.

2-After some special verbs like: want,ask,wish,promise,order,tell,advise,encourage.....+n/obj+...to

e.g:Does he encourage his wife to attend those spiritual classes?

3-There are so many exceptional points but it takes an ocean of time.
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How can I learn which verb use gerund or infinitive?
There is no rule. Most grammar books have lists of the most common ones. [url=http://owl.english.purdue.edu/owl/resource/627/04 /]HERE[/url] are lists of some.

As Mr Mister Micawber said there's no rule saying the specific verbs are followed by (ing)/(to) but I think most of the verbs expressing the" INTENTION or PURPOSE" of an action going to be done need to be followed by "TO"

such as:want,intend,plan.decide,wish,hope,promise,try*mean*,beg,agree,expect,swear,claim,be able,...

1-Does he plan/decide/intend/wish/agree to travel round the world alone?

-But after the verbs like: enjoy,avoid,risk,imagine,keep,dislike,admit,consider,feel like,deny,delay,appriciate,excuse,finish,fancysuggest...we need "ING.

1-I've never enjoyed/avoided/denied working in a field.
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