As an ENFj, I've had problems with getting along with ISFps. This is what I have learned:
The best advice I can give - smile and nod. They don't think badly of shy people, because they often consider themselves to be quite shy. Observe an INTj who fails to laugh on command. They just smile politely. No need to be very expressive around introverts... I mean, if you try to have very good relations with introverts, it's better to be the active side, but if you act introverted, they certainly won't blame you, because they can relate. Just look shy and they'll understand. And don't look angry/mean/annoyed. They can sense it with their Fe creative. This is how their mind works - they gather emotional data from around them. Just look indifferent. Keep telling yourself that it's just a moment in time, nothing more. Their thoughts and actions are more momentary and less linked to a process, so for them, the moment really is "just a moment". Try to adopt the same attitude, because it helps you stay on the same level with them.
Try to keep them happy. don't say negative things about the past, present or the future unless you definitely have to. If you do have to do that, try to give a solution to the problem. You don't want to be the person who ruins the moment for them. They work really hard to keep themselves happy, but due to the IP temperament and Fe creative function, their mood is very easy to ruin. They really dislike people who keep on ruining their mood.
I don't understand ISFps and I have a hard time agreeing with them, but it usually doesn't make a difference for me, so I avoid trying to convince them that they are wrong. The INTj approach works here too - INTjs won't argue anyone into believing anything. They'll look indifferent in a shy way. And the opposite - when someone tells an INTj something that they DO like to hear, the INTj still won't respond. They just smile in a shy way. It's the Fe people who always verbally agree with things, but Ti people don't do this so much. At most, the Ti people nod and smile. This behavior is easy to adopt.
So to get along with ISFps, just smile and nod and the rest of the time look indifferent. Don't pout and don't argue.
It actually works so well that ISFps start treating me like I'm an INTj. They start trying to cheer me up and when I give them a shy smile, they think they succeeded and they feel happy about it. (I read body language too). It's wise to uphold the illusion that you really are an INTj and that their Fe is working on you. It will keep them happier and this way it's easier to get along with them. One more thing - ISFps are surprisingly forgiving of a bad outfit when they realize you're just a goofy INTj who doesn't know any better. This make the aesthetics side of PoLR more tolerable.
I can occasionally hang out with my ISFp sister so that's it's actually pleasant and I improved relations with my ISFp mother. The smile and nod-relationship seems very superficial and fake, but it's helluva lot better than not having any relationship with your own mother.