The most common problem I see with people's Tricep training is that they often only stick to cable exercises and they often use only light weight/high reps for 'Toning' the muscle. This is ineffective for a couple of reasons:
1) the Tricep is predominantly a fast-twitch-fiber muscle group, meaning it responds best to lower reps/heavier weight
2) you cannot 'Tone' a muscle with any exercise. You only can either build (add) new muscle that wasn't there before, or lose muscle/make it smaller. The shape and level of definition in a muscle depends on how lean you are ie. how low your overall bodyfat is. But you won't see ANY 'tone' if there's no muscle there in the first place! And this is why most people aren't seeing changes in their tricep gains: they're not hitting it effectively.
Here I go hard on both Lying Tricep Extensions and Pushdowns, demonstrating that lower reps and more challenging weight to overload the target muscle really brings out definition in exactly the area you want it ⚡ ⚡ Try hitting Triceps with the maximum weight you can use in the 6-8 Rep Range ;)