Having leveled quite a few chars (mostly duoing) i can tell you the following:
1. XP Turn ins are King - use and abuse them in every way possible. plan ahead. dont waste them - be smart about when to turn them in. comes with experience. (scenario to clarify: level 35 char - got 2 sets of turn in items ready - turn in for both in the same town - 9 bubs left till ding - here id totally stay out on the field n grind enough xp to just ding from 1 set so i can immediately turn in the other - which means ill end up at lvl 36,65ish and can go ding again on my way of farming the next set so i can turn in again) this includes phoenix eggs. spend them wisely. (last level on casters before you get a new nuke for instance.)
2. MobTypeBonus is glorious - trust me. its way more valuable than task ticks, having a favorable dmg-type or whatever. killing mobs with 200+ xp bonus is just stupidly efficient even if they whack you for + and you hit them with -.
3. Use Buffpots - lvl 10 is achieved rly quickly. from this point on you should use buffpots at all times. the relevant ones that is. that means for casters ull want acuity and replenishment up at all times - usually u wont need dex since all you want is your bang/buck (or power in this case) ratio to be optimal. on lvl 30 u should have enough money to spend it all on a combined forces barrel. of course this tip benefits some classes more than others.....but unless you play a sham/cler/drood im positive that using the power buffpots is essential in optimizing your lvling experience - and every piece o gold spent on buffpots is well worth it.
theres more but i kinda feel like those 3 points are the pillars of quick n fun solo/duo leveling.
bonus tip: dont focus too much on killtasks - take em as a bonus and keep them on your radar...but dont spend much time on them.
bonus tip 2: once you are lvl 35+ make sure to suicide every once in a while in rvr - RR2 helps a TON during leveling by granting you access to crucial RAs.
bonus tip 3 mini edition: make sure to spend your "free realm ability point" that you get at...level 10 i believe (feel free to correct me on that i rly dont know
) on serenity or tireless depending on which resource you rely more on.