Upgrading the spell will increase its duration on the battlefield (the level 3 Jump Spell lasts three times as long as the level 1 one).
Make sure to always use the Jump Spell near Walls! If you accidentally use the Jump Spell elsewhere, it will have no effect, wasting the spell, your Elixir and your time.
This spell is more effective on doubled or tripled Walls; otherwise the spell is not utilized to its maximum capability, making it much less valuable to use.
The effects of the Jump Spell do not change if you drop more than one spell in the same area, so be careful not to use two in the same place!
Especially with the new Wall Breaker AI, Jump Spells can be quite useful for getting Troops deep into the interior of a base. Once Wall Breakers have initially breached the exterior Walls, any new ones tend to be attracted to adjacent cells rather than those behind the breach. A Jump Spell, however, can be placed behind the initial breach to quickly allow Ground Troops access to the second layer of the base where the storages and heavy defenses (Mortars, X-Bows, etc.) are typically positioned.
The level of the Wall does not matter to the Jump Spell; Troops will be able to jump over Walls of any level.
Jump Spells have no effect whatsoever on air units, as they already ignore Walls since they are flying. This also does not change the behavior of Hog Riders or Wall Breakers in any way.
The rings that circulate around the illustration of the Jump Spell is to resemble the action when troops jump over Walls.
The spell acts like a better (albeit temporary and more expensive) Wall Breaker.
The 17 Jun 2013 update changed the behavior of Jump Spell. Prior to the update, the level 1 Jump Spell only affected Troops that required 4 or less housing spaces (Barbarians, Archers, Goblins, Wizards), with the remainder requiring level 2 to jump Walls. As of 17 Jun 2013, all Troops are able to use a level 1 Jump Spell, with level 2 doubling the spell's duration.
As in the 3 Jul 2014 update, the Jump Spell adds a better "battle flow." If troops sense a better route, they will now walk over to the Jump Spell, so if they are close by, they can still walk over to the Jump Spell, even if they were not there when first placed. In other words, the old Jump Spell determines the area of troops that can jump over Walls, while the new Jump Spell determines the area of Walls that can be jumped over.
Although the Jump Spell can be upgraded to level 2 in the level 6 Laboratory, only Troops and Spells that are already unlocked will appear in the Laboratory upgrade interface. The Jump Spell will not appear in the Laboratory until the Spell Factory has been upgraded to level 4 (which requires Town Hall level 9). Most players already have a level 7 Laboratory by that time; if so, the first upgrade will be available as soon as the Spell Factory level 4 upgrade finishes.