I'm level 20, and I want to try for the chocobo quest in Jeuno. How do I get to Jeuno on my own?
Getting to Jeuno solo at level 20 is a pain in the ass. In fact, getting there in a party (even alliance) with others your level will still be a pain. Why? All of the areas leading into Jeuno are massively difficult for people your level. In Sauromugue Champaign you have killer skinks, Rolanberry Fields has Drooling Daisies, and Batallia Downs has the lovely Sabertooth Tiger... So regardless of the way you go, you'll have a helluva time getting there.
Personally, I would say that going by way of Sauromugue Champaign is the riskiest simply because those skinks aggro, link, and move so quickly. They probably aren't much worse at this level than the tigers in Batallia Downs, but at least the tigers stand out strongly against the background so you can easily spot them in the distance.
Rolanberry Fields by way of Pashhow Marshlands, Konschtat Highlands, and Gustaberg North seems pretty common to a lot of players (they start out in Bastok and just head north), but my personal favorite is to pass through Jugner Forest to Batallia Downs. Jugner has some nasties in it, but most of the really aggro things are easily avoided except for the gobs which I can generally outrun anyway. I like Batallia because the enemies stand out strikingly against the landscape making them much easier to avoid.
Some people claim that by reducing themselves to a very low level (like 1 or 2) they can just run through these environments and avoid all battles (like the enemies are sizing them up and determining they are too weak). I personally haven't had the guts to verify this.
How do I get to the hidden beach at Valkurm Dunes?
The hidden beach is a pretty cool place to level between 18-22, and it also spawns everything you need for your sub-job quest. Additionally, it branches off to other places needed for quests/missions later on.
If you look at the [map] for Valkurm Dunes (you do have one, don't you? ;-) in the upper-lefthand corner near C-6 you will see a little squirly turn. Go there and you will find a passageway leading to the hidden beach.
Be warned though, gobs spawn profusely around that area (making it another good place to level up in parties 19-22) so be careful getting there.