Repeating "to" and "will" in enumerations of verbs

Should I use the second "will" in constructions like this one: "it will definitely help you and will make the text more readable"

And should I write "to" before every infinitive in enumeration, or only before the first one, e.g. "it helps to develop and test" or "it helps to develop and to test"? Could this example be influenced by the fact that "help" can go with to-invinitive and bare infinitive, and with other verbs the rule would be different?

It is not necessary in your example sentence to repeat will but doing so serves to emphasise that there are two consequences: this will happen and that will happen (cf. this and that will happen).

If, on the other hand, one of the consequences itself contains the conjunction and, then it is advisable to repeat the will to avoid momentary ambiguity. So:

• It will definitely help you and your colleagues and will make the text more readable.

is preferable to:

• It will definitely help you and your colleagues and make the text more readable.

The same principles apply to the repetition of to.