[tdh]

In my experience what you need to look for are mobs that check High Def. Those are the ones you're going to get Skill Ups on. It seems that I rarely get Skill ups on mobs that don't check High Def, and almost never get in on Low Def mobs.

This is the main reason that people Skill Up on Crab type mobs due to the DEF UP TP moves they have to make sure they stay High Def mobs.

Depending on your actual job level, and your weapon level, you can take a few paths to catch up a weapon solo. The higher you are, the better you have Skilling since you have much higher survivability.

Valkrum Dunes - You can use Crab mobs here. They will use DEF up moves, and are probably going to serve you quite well up to about Skill Lv.50 or so. (You can of course go a little further with some jobs, or weapons.)

Qufim Island - I've used the Island to level weapons up to Lv.80 or higher. (Great Axe, Great Sword, and Marksmanship I know of for sure.) After this point I headed out to the 2nd Jungle. Using Mandy's and Goblins to level a weapon up to Lv.100.

For a lot of jobs, this is the end of your solo Skill Ups for melee, and you may have to find a LS mate to tank for you so you can still skill up past this point. This is all dependant again upon your job and what weapon you're working with. Great weapons are a real pain to Skill Up solo due to their high delay, and some MP users have a hard time at it because they spend more time casting spells than swinging their weapon.

As RDM I was able to solo Skill Up Sword and Dagger to Lv.200, but at that point I had to find parties since I was spending more time casting Phalanx and Stoneskin just to survive. Keep a look out for /shouts in Jeuno. There are often people trying to build Skill Up parties, and they will give a level range to let you know if you are in their range. Some of them are trying to break latents for WS Quests, so they spend an hour or more going at it so you can make some real progress.