A very common error that we come across quite often is the use of ‘will’ made twice in a single statement while referring to two future events simultaneously.

If I will get that packet by tomorrow I will send it to you.

Here two future events referred to are:
* I will get that packet
* I will send it to you

If you have to talk about two such events together then the first event should always take simple present form and the following event should take ‘will’ (future) form.

If I get that packet by tomorrow I will send it to you.

Here are a few more examples:

If the taxi does not come soon, we will miss the train.
When it gets warmer the snow will begin to melt.
If I drop this watch it will break.

He will help you if you ask him.