Sceptile Mega has to be one of my favorite Megas. Thanks to Pokemon_lover0523 for suggesting it. There are two major mega sets I would use on this guy:
Special set:
Sceptile
Sceptilite
Modest/Timid nature
252 sp attack 252 speed 6 hp
Leaf storm
Dragon pulse
Protect
Focus Blast/ Giga drain
Really with this set all you have to do is Mega evolve, protect, and proceed to blow things up. Leaf storm and dragon pulse have great coverage together. Protect is for getting your mega boost safely as Sceptile is a bit lacking without it. The last move is your choice; Focus Blast gives you a way to deal with ice types that will wreck sceptile otherwise but it's not very dependable. Giga Drain can restore sceptiles health which can be nice. Take note however that Ice types and the recoil of leaf storm will force sceptile to switch constantly, so be sure to have plenty of walls to switch into and Mega it early in the battle as you will have more maneuverability when you have more pokemon.
Physical set:
Sceptile
sceptilite
Adamant/jolly nature
252 attack 252 speed 6 hp
Swords dance
Leaf blade
Drain punch
Dragon claw/dual chop
Upon Mega evolving Sceptiles attack rises to a respectable 110, making a physical set possible. Swords Dance and leaf blade are must haves- sword dance gives Mega Sceptile the power it needs, because 110 attack is good but not exactly impressive. Leaf blade is STAB and has high power and accuracy, as well as high crit rate on the side. Drain punch is sceptiles best option against Ice types that want to give it trouble, as well as a recovery move. The last move will also be your STAB dragon type move. Dragon claw is accurate and dependable. Dual chop does the same amount of damage but is a little less dependable with 90% accuracy but In turn hits twice, breaking substitutes, sturdies and focus sashes, as well as giving sceptile two chances to get a crit. This Sceptile can deal better against ice types than its alternative set but with drain punches low power you must be careful. One more thing; you want to keep this sceptile in battle, rather than switching out often, because of sword dance. This Set is also surprising as Sp Mega Sceptiles are more common so this set can take your opponent completely by surprise.
Hope this will help you raise up some strong Sceptiles.