a question:

if the ruler of 1st and 7th are in square aspect, and the question is about whether a relationship will take off, what is the positive that may overcome the square aspect? what should i look for?

Well,

as far as i know, if the aspect is applying and there is a reception between the significators, then the relationship will take off. I know that a square indicates obstacles, problems of some sort and delay. Is this correct?

that`s right, Zorana..obstacles. Both people are willing thou.
How many ways of two planets to be in mutual reception are there? Is it only when, say, Moon is on Capricorn and Satirn in Cancer(if the planets are Moon and saturn) when we talk about mutual reception? is there any other ways ?

I think so ...

f.e. we could have the ruler of the Asc, lets say the Moon, be in Libra and Saturn, as the ruler of the VIIth house, in Capricorn - which would form a square, as you have mentioned. The Moon exalts Saturn, but Saturn receives the Moon into it's exile. This is a mixed mutual reception.
Mutual reception by ruling sign is the strongest. There can be reception (in order of strength) by sign, exaltation, triplicity, term, or face. And, of course, by exile and fall.

thank you, Zorana