In formal English, you use should and would like this:

If I should go to the party next week, I would take cookies.

This is very formal.

Less formal, but still educated sounding would be:

If I were to go to the party next week, I would take cookies.

95% of the US population would say this instead:

If I went to the party next week, I would take cookies.  OR

If I go to the party next week, I would take cookies.

So, pick the one you like.  It depends on how "correct" you want to be.

Hi Iqrar.

You use "should" to:
1) Express that something is probably.
   Ex: "She should be there at 7pm"
2) Ask for some advice.
     Ex: "Should I take that job?"

And "would" uses for:
1) Wondering about the probabilities
     Ex: "How would you do that?"
2) To offer or ask for something
     Ex: "Would you like some tea?" or "Would you help me, please?
3) Hypothetical situations
     Ex: "I would like to date her"

I hope you understand :)