Low Elo

For junglers that rely more on auto-attack, I go x9 Attack Speed Marks, x9 Armor Seals, x9 Magic Resist per Lvl, x3 Armor Quints. This gives 15% Attack Speed, 25 Armor, and 24 MR at lvl 18. All Jungle camps just do physical damage, so having the extra armor will help and allow you to deviate from the standard cloth armor, x5 health pot build. For spell-casting junglers, I'll swap out the x9 Attack Speed Marks for x9 Armor Marks to get a nice 34 Armor just from runes.

Good junglers to start with:
Warwick - probably easiest autoattacking jungler as his passive allows him to jungle safely. However also makes him one of the slower junglers in terms of jungle clear speed and his ganks before lvl 6 aren't scary
Udyr - fast jungle clear, and provides lots of CC for teamfights while being very tanky, also can gank early

These probably are among the easier junglers, but just about every champ can jungle. Practice the jungle route in a coop vs ai game or custom game unless you are playing a premade with friends.

I know there are some apps out there for the iPod/iPad/iPhone that can keep timers. Generally, I just keep an eye on the in-game timer (upper right) and add from there. Small camps are 1 minute, buffs are 5 minutes, dragon is 6, and baron is 7 minutes. Keeping timers is like any other skill you pick up playing the game, like map awareness on the minimap, timing wards, last hitting, knowing your full combo damage, etc.

One last great tip i can suggest is use custom bot or coop vs ai bot games to try out any champ in the jungle. When you get to be experienced enough, you will find that you can literally jungle with any champ now. The more you jungle the better you'll become and understand jungle routes. ALWAYS ALWAYS ALWAYS take smite. If you are jungling, and you don't have smite, you are trolling your team... No exceptions

My question is why are you running oom a lot that you need a clarity? No champ in the game should EVER take clarity. The effectiveness of clarity inevitably drops until it becomes pretty much useless by late game as champs that needed mana would have built up mana items or use blue buff. It simply is overshadowed by every single other summoner spell in the game while helping maybe the tiniest bit early game during laning phase for a small handful of champs.

For champs that lack tons of CC, I like to use exhaust as the second summoner. I'd consider ghost pretty much only on Olaf or Shen. Flash helps for a gap closer (Alistar, Amumu, Rammus, Fiddlesticks, warwick, udyr). Gank heavy junglers, definitely getting exhaust is a huge help in securing kills for your team on the ganks.

At higher levels, bandage toss is too easily dodged by players. For amumu a more reliable engage when ganking a lane is flash-ult-bandage toss. This gives a full stun duration of both of Amumu's CC which should give adequate time to secure a kill.

For jungling and junglers, I still feel that you want to take summoners that will help you do your job better - that is secure buffs and global objectives and ganks. Clarity offers very little in terms of a gank and is only useful if the lane your ganking is doing really badly that they are OOM. Flash can be used offensively and defensively so helps in closing distance suddenly and escape from a bad situation. Exhaust is a slow that can only be stopped with cleanse (oranges, spell shields, qss do nothing for exhaust) - this helps secure kills in ganks, and if you took the passive make the target even easier to kill. As an added bonus, exhaust is also amazing defensively as it reduces damage the target deals significantly.

Clarity just doens't give the same utility for a jungler to do their job compared to either of the above. Teleport is situational (if they have a strong split pushing ability - like Shen, TF) then someone on your team should get teleport to be able to follow them - usually Top lane. Heal gives a stat every champ will need in teamfights, which is more health. Ignite can be used if you are playing a carry jungler but this will make for unbelievably strong ganks with Red buff.