..who don't wear proper clothing (i.e. tight & transparent) and also wear hijab? and they are sisters whom I do not know personally. Just randomly seen in university or so. should I just go and advise them straight forward (since i might never see them again and this might be my only chance) or should I just give indirect advise? I hope to be able to convey without neglecting the حكمة part

i have actually created a thread on this topic previously in this section and as you have correctly observed as many of us have all over the Islamic world aswell as western world that many of our sisters unfortunatley are using the hijaab as a fashion accessory.
Much of this may come down to knowledge and also ignorance. But the fact of the matter is that it is upto our dear sisters to remind them and inform them in the best of ways that they must not abuse or misuse the beautiful and sacred hijaab and that they must wear it as it is prescribed for them to wear it by Allah and not like how shaythan wants them to wear it as a fashion accessory to attract even more attention upon themselves than sisters who don't wear it at all.
Just the day before yesterday a sister who works near where i do and also lives near me wore a skirt just upto her knees with see through tights with a hijaab on her head. This truly shocked me because i never thought that a sister would go that far whilst wearing hijaab and i just did'nt know what to think in seeing this but it did truly sadden me that this is how far things are going nowadays.
Sisters you must inform other sisters who may not have the correct knowledge and understanding in the most beautiful of manners as prescribed by Allah in the Qur'an. You should:
1. Start off by breaking the ice somehow and talk to them in a friendly manner and maybe the second or third occassion invote them to a sisters circle or halaqa and if they attend then talk about the beauty and true essence of hijaab and its sacredness.
2. Take their number and e mail and send them weekly Islamic reminder texts and beneficial Islamic to their e mail.
3. Talk to them about Islam maybe for a short while or even few minutes whenever you come across them and don't mention the hijaab subject straight away maybe after a couple of occassions talk about the beauty of hijaab and how it should be worn in a proper manner but do it in an indirect way for example: We should do this or that not you should so as to make it seem like all sisters should do things this way so they don't feel its targeted right at them because a lot of the times if people feel they are being targeted then their defences may come up.
4. Once you have spoken to them on a number of occassions and have a closer friendly relationship with them then maybe you can bring up the subject when you feel is the right and appropriate time. When talking about this subject do it in the best of ways and in a very gentle manner so that they start to appreciate the true essence and beauty of hijaab and that they should wear it in a proper manner with appropriate clothing.
May Allah give all of us both our brothers and sisters the ability to dress modestly and simply. Ameen
:wa: