Every match had chances for Pakistan especially except the first match Pakistan had chances to win the remaining two matches but Pakistan could not capitalize on those chances.
The first match may have been limited to short overs due to rain and Australia's target of 94 runs in seven overs was quite impossible for Pakistan due to which the first match did not meet the target despite Pakistan's best efforts.
But the second match was the most likely for Pakistan to win the match but Pakistan could not win only because of poor batting performance otherwise the match would have been tied 1-1. In the third match, Pakistan won the toss and could not capitalize on it, as a result of which Pakistan had to lose the T20 series by 3-0.
Pakistan had chances to win series but they did not take them. Except for first match cut short by rain Pakistan could have won other two. They blew their best chance in second match due to poor batting. In third match winning toss was not enough and Pakistan lost series 3-0 to Australia. To improve I think Pakistan should focus on the mistakes which they are making. And should fix them. And main issue is consistency. They have no consistency in their playing they should focus on it too.
In fact, basically, Pakistan cannot compete with Australia in limited overs matches, especially in T20, if Pakistan is an ODI or Test series, then in that case, Pakistan has a high chance of winning in long overs series. Just as Pakistan won the ODI series, Pakistan's chances of winning the Test series would have been much higher.
But in the T20 series, Pakistan cannot bat aggressively or even if they bat aggressively, they cannot sustain the batting for a long time, due to which Pakistan cannot easily meet the target of runs in limited overs by Australia. Or even by batting aggressively, Pakistan can't give a target that is enough runs to win, so Pakistan can't compete with Australia by performing well in the T20 series.