I got a mastery 7 Skarner too (just haven't used the 3 tokens yet) and i as well do jungle, and top, and do about the same champions.
It's hard to give advice without seeing your play, but we can work and talk Skarner for a bit cause I consider Skarner the secret strong champion.
Typically I like to gank as soon as I hit 3, so I look for a lane shoved up. (Usually you can gank one of the lanes cause Skarner hits 3 really fast). Always important to have them crystals as you might be aware of. Typically, I always build Skarner with Warrior>Triforce>Frozen Mallet. If they heavy AD, then I get Frozen Mallet as a 2nd item, and get Triforce as a 3rd item. (Trust me, Frozen Mallet on Skarner is literally the key to success with him). Anyhow, build against whatever damage they are if they are AP, or AD damage.
Sometimes it's a good idea to ward the enemy junglers camp whether it's their chickens, blue or red buff, just do it. Always try to get the scuttle crab in the river, and predict the enemy Jungler's whereabouts.
Ganking mid lane is easy and for some reason, a lot of people in every elo fail to do it correctly. Most go through the mid lane bushes. NO, don't go through the bushes, that's the warding area, go behind the wall on their side, and do it.
Also, here's probably one of the coolest tricks to jungling and getting kills, easy with Skarner. Ok, lets say the enemy top laner doesn't have TP, or has used teleport recently. Gank him (don't go through the river to gank him, go through the tribush). With Skarner it's easy, land your E, then stun his ass, or simply ult him (try saving your ult on the first gank). Ok, so if you kill the top laner... This is where it gets spicy and what I have been doing. Tell your top laner to come with you, and camp the bush near Krugs (rocky monsters) and set a ward out in the lane. Wait about a minute, the enemy top laner will be walking back to lane, and come through that bush and kill him again before he reaches his turret!!! This trick is so cool, and can net 2 kills if you are good enough. Of course, it requires the enemy top laner not having teleport up, or flash (although it's possible to still kill him with his flash up with Skarner if you can get your ultimate off before he flashes).
Skarner is good at taking dragon, a lot of champions can do it after level 4 if the health plants are nearby, but I would suggest get the first part of your major jungle item first.
If you see the enemy jungler gank top lane? You should punish that and take the dragon, or use that time planting a ward in his jungle, or taking a camp.
Anytime you see the enemy pushing your team to the turrets, it's a good time to attempt a gank usually.
I mean really, this should be common sense but yeah
