Choosing the right one:

Formally," if " and " whether " are used

in very specif examples,and give senten-

-ces different meanings. 

 Good tips about them ?

http://www.macmillandictionary.com/dictionary/british/tip_1

Use If when you have  conditional sentences.

Examples:

Bob will meet Mary next week if she accepts

his invitation to have dinner with him.

Peter would pay for Jane's lunch if he had

more money in his wallet.

The children would have enjoyed the park

much more if the rain hadn't started so early

in that afternoon

Use whether when...

...there is an infinitive with "to"

Example :

Lucy wasn't sure whether to invite David

and his new girlfriend to her wedding party.

...there is a preposition

Example: 

The students wanted to have a conversation

with their History teacher whether she could

discuss a bit more about the recent Terrorist

attacks.

...using the word "or "

The reporter didn't know whether to ask a

formal or informal question to the French

president ?

Click on the link bellow for more examples

with whether,ok ?

http://www.macmillandictionary.com/dictionary/british/whether