One of the easy ways to eliminate the more extreme abuses is a line-of-sight limitation. You can only teleport to a location if you can currently see it. That puts a hard cap on the range of the effect, and introduces opportunities for opponents to disrupt it (fight indoors, obscure their vision, etc). Teleporting somewhere you can't see isn't a really good idea anyway, because you have no idea if the laws of physics will even permit you to exist in that space (ending up inside a solid object would be game over for you).
For an extra twist, you can limit how close you arrive to your target point to be dependent on how clearly you can see that point. For example, stick out your thumb and hold it at arm's length, covering up your target. The area of your thumbnail represents the size of the area in which you might end up. When teleporting across the room, that area is only a few square inches so accuracy isn't really an issue. Teleporting to that hill far in the distance could be a problem, though. That same thumbnail-sized area is bigger than the apparent size of the hill, so you might miss your target completely and end up somewhere undesirable.
Any sort of teleportation is going to be rather overpowered in combat, simply because it lets you evade attacks nearly perfectly. The most straightforward way to reign in the usefulness would be to make teleportation not an instantaneous process. The caster has to focus/concentrate/channel for a period of time before teleporting. This prevents it from being used reactively, which is where most of its overpowered nature comes from. It also leaves your caster vulnerable just before they teleport, which means it has to be used much more strategically. Great for sneak attacks or initiating fights but once the fight starts, you can't fight invincibly like Nightcrawler in X-Men United.
You can even incorporate this into the lore if you want. Teleportation is a form of shadow magic. The caster channels their magic to send their shadow to a distant target location. Once the shadow reaches the destination, the caster will suddenly find themselves there as well (like how you can travel to the other room and turn on the light to make your shadow appear at your location, only it works the other way around). The shadow travels at a certain speed, say, 10x the speed of the caster. The caster would then have to channel for some brief minimum length of time plus however long it takes for the shadow to travel from A to B. That won't completely preclude its use as a combat escape mechanism, but will require your character to earn themselves enough breathing room to complete the cast.