Guide from 0 to 100

1. Use a recipe up until 1 lvl before cap. (I.e.: I would stop at 49 for a 50 lvl cap)
2. Do not bother with a recipe until you are 8 lvls from cap so you can get a skillup from a failed synth. (For a 50 lvl cap, adv. support from 42.0 to 44.0 and reg. support from 44.0 to 45.0)
3. I do not recommend break synthing on Nasomi as it seems like crit fail is pretty high. Would be great if others could confirm/negate this point.
4. Always compare the cost of every recipe on a per unit basis. If you can desynth them, divide the cost of a stack of mats per 24 and if you can't divide it by 12.
5. Do not follow this guide blindly

0-2: Copper Ingot
2-6: Copper Hairpin (Synth/Desynth)
6-8: Brass Ingot
8-12: Brass Hairpin (Synth/Desynth)
12-17: Silver Ingot (Beastcoins Recipe)
17-26: Silver Hairpin (Synth/Desynth)
26-31: Desynth Silver Ring (Tons are available due to fishermen so buy the rings, desynth them, and then synth the rings back)
32-36: Mythril Ingot
36-46: Gold Dust
46-50: Gold Ingot (4x Gold Beastcoins)
50-57: Gold Hairpin (Synth/Desynth)
57-59: Gold Ring (Synth/Desynth)
59-66: Hydro Patas (Synth/Desynth)
66-68: Mailbreaker (Synth/Desynth)
68-72: Moonring Blade (Synth/Desynth) - Requires Smithing 53
72-73: Ashura (Synth/Desynth)
73-79: Gold Buckler (Synth/Desynth)
79-82: Rapier (Synth/Desynth) - Requires Smithing 28
82-92: Muscle Belt (Synth/Desynth) - I suggest starting at 82 if you have Apron + Spectacles + keep doing until 92 because it's so cheap.
92-95: Lv 72 Ring
95-97: Verdun
97-100: Lv 74 Elemental Rings