Like was said on the page about the Equality Principle, one of the most important things in math is to give up on the "mantras" and think in a more logical and natural way.
With this, we ask: which equivalent fraction of the first fraction has the same denominator from the second fraction? (Which fraction with denominator 6 is equivalent to 2 over 3?)
To find it out, we make a division to know for which number to multiply both the numerator and denominator:
$$\dfrac{2}{3}+\dfrac{?}{6}$$We know that 6 divided by 3 is 2, so we can multiply by two the numerator:
$$\dfrac{2}{3}*2=\dfrac{4}{6}$$Now we can sum the fractions with the equivalent of the first one:
$$\dfrac{4}{6}+\dfrac{2}{6}=\dfrac{6}{6}=1$$This is a way easier solution compared to using the Least Common Multiple, a mantra that is very un-intuitive and over-complicates a simple problem like this one...