Some teleportation ideas that I've used:

Subtlety

- Teleportation is loud: dimension door is a 'bamf" sort of noise (conversation level), while greater teleport is like the clash of steel weapons, and plane shift is a thunder that shakes the foundations of mountains.

- Teleportation causes noise before you appear. A Listen check can determine the approximate destination of an inbound teleportation. Longer distance teleportation causes more warning time, and also a louder sound. Tactical teleportation spells are much, much harder to hear, since they're short-distance and since there's a battle going on which tends to hinder Listen checks.


Targeting

- You can teleport anywhere you can see, or where you have personally left an arcane mark.

- You can also teleport to established teleportation circles for which you know the pattern. Well-known circles are usually guarded.

- Other than LoS and known circle patterns, you can't teleport to places you haven't been. Exploration by conventional means is a state-sponsored activity.

- Plane Shift only works in locations that are coterminous with that plane. If you want to visit the Plane of Fire, you might need to find a nice active volcano, or an underground coal fire that's been burning for a century.

- It's comparatively easier to create a location that's coterminous with the lower planes (the fiendish realms), because it's comparatively easy to inflict suffering on mortals. Details for this sort of thing are suitable for a horror campaign.

Spoiler: More Horror
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At a deeper level of horror, you can use a living humanoid's intestines as a temporary gate. This limits the duration of the gate, and the size of creature which can pass through, but it makes for a memorable session when the PCs finally get around to "closing" a gate.

Important: only Fiends can pass through this type of gate. Only Fiends and cultist NPCs can create this type of gate.

Mechanically, this creates an asymmetry between what Fiends can do and what PCs can do.