If you don't have skill books, I would highly recommend you save your SP until at least 150 so you can max the skills as they come. Your core skills (first 40-ish levels) should be maxed before putting SP into other skills.
100: 1 BStep (1), 1 Shadower Instinct (1), 1 Toxic Venom (1), 1 Sudden Raid (1)
101: 1 Shifter (1), 2 BStep (3)
102: 3 BStep (6)
103: 3 BStep (9)
104: 3 BStep (12)
105: 3 BStep (15)
106: 3 BStep (18)
107: 3 BStep (21)
108: 3 BStep (24)
109: 3 BStep (27)
110: 3 BStep (Max)
111: 3 Dagger Expert (3)
112: 3 Dagger Expert (6)
113: 3 Dagger Expert (9)
114: 3 Dagger Expert (12)
115: 3 Dagger Expert (15)
116: 3 Dagger Expert (18)
117: 3 Dagger Expert (21)
118: 3 Dagger Expert (24)
119: 3 Dagger Expert (27)
120: 3 Dagger Expert (Max)
121: 3 Shadower Instinct (4)
122: 3 Shadower Instinct (7)
123: 3 Shadower Instinct (10)
124: 3 Shadower Instinct (13)
125: 3 Shadower Instinct (16)
126: 3 Shadower Instinct (19)
127: 1 Shadower Instinct (Max), 2 Toxic Venom (3)
128: 3 Toxic Venom (6)
129: 3 Toxic Venom (9)
130: 1 Toxic Venom (Max), 2 Shifter (3)
131: 3 Shifter (6)
132: 3 Shifter (9)
133: 3 Shifter (12)
134: 3 Shifter (15)
135: 3 Shifter (18)
136: 3 Shifter (21)
137: 3 Shifter (24)
138: 3 Shifter (27)
139: 3 Shifter (Max)
140+: Whatever you want.
Total by 200:
30/30 (Maxed)
30/30 (Maxed)
30/30 (Maxed)
30/30 (Maxed)
30/30 (Maxed)
30/30 (Maxed)
30/30 (Maxed)
10/10 (Maxed)
30/30 (Maxed)
5/5 (Maxed)
A Shadower's Core consists of 5 skills, 6 if you want to include Assassinate (which is good at lower levels, but worsens as you pass the 45k range. I'll explain in a bit).
1. Boomerang Step. This is the bread and butter of your core. Without this, Shadowers lose everything. It provides huge iframes, chains perfectly with Midnight Carnival, and does heaps of damage. I would macro this with Midnight Carnival, and also put it on a separate key as well (I have it on Shift and the macro on Ctrl). The macro you use when you're standing still, ie, bossing, LHC, Stronghold. When you're just killing lower leveled mobs for drops (event drops, etc) you want to just use BStep as the macro can interfere with your jump attacking. You can macro this with Assassinate for superior 1v1 damage output (it cancels Assassinate's final 100% crit chance hit if used right after you do your initial 3 hits; in a macro, put BStep after Assassinate), and also Phase Dash for extra mobbing/rushing, as both have moderate delays after individual use. It also chains with ME, which is useful at bosses where the iframes will matter and you can't necessarily afford to sit in one spot holding down ME.
2. Dagger Expert is self explanatory. +30 Weapon ATT, 90% mastery (you have a passive 20% mastery because you're a melee class), and a bunch of Avoid is what is important.
3. Shadower Instinct. This is your buff you'll be spamming, since it only lasts
one minute. It seems low, but it's a fair tradeoff considering it gives you a whopping 50 ATT at level 20, which stacks with every other buff in the game, including Karma (your 2nd job buff? Remember?). You need 5 "Body Count" to get the full effect (the little red orbs over your head), which only start appearing once you get one point into this skill. At level 1 it gives a stacking 31 ATT buff for 1 minute (same duration for all levels), so get a point into this fast! Make sure you have it up all the time, sometimes I forget to cast it ;_;
4. Shadow Shifter. 45% Dodge Chance is good. Enough said? Enough said.
5. Toxic Venom. This freaking amazing passive lets your DoT from Venom STACK. Also increases the damage per tick. Not only that, every stack makes its
own line of damage. You're probably thinking "who cares?" but if you're a godly funded Shadower, you will understand. Instead of fusing, lets say, 50,000 damage x 3 into one big number of 150,000, it shows up as 3 lines of 50,000. This means that if you were to somehow hit over 333k damage per tick on Venom (which would suggest you have a 200k range or so, luls), you wouldn't lose damage to the damage cap. Obviously for most of us this is pretty insignificant, but I thought it was pretty cool ^_^
(6.) Assassinate. If you've got less than around 80-100k maximum range, this skill is actually very good to use. The reason you don't really want to use it past the upper ranges listed (100k range zzzz) is because you'll lose damage as it will hit max damage every single time you use it, and only to one enemy. If you had used BStep instead (which has a much shorter delay), you'd do more damage to more enemies. Particularly, this is important at places like Stronghold or Lionheart Castle, but in any case, for most people this will be pretty darn important to max after your initial 5 skills. Assassinate can be cast outside of Dark Sight now (yay) but if you cast it while in DS you do 250% of the damage you would do without DS. This is freaking awesome. In addition, if you have 5 Body Count, then it will do an additional 2.5x damage (which stacks with DS...) At 40k range or so, you have a good chance to hit max damage consistently if you use both DS and your 5 Body Count. This is really really good at LHC if you haven't gotten supergodly damage, as well as bosses in the same scenario. Remember that you're vulnerable during Assassinate, so always keep an eye on your health!
Nines!
Note that, by 140,you'd have maxed your core skills. So what do you do after 140? Max everything else, then max all your 1st, 2nd, and 3rd job skills you skipped out on (yes, including Lucky Seven). At level 187 you max out every single skill you have in the entire book, so there isn't really much to do past that. I'm currently sitting on 35 SP (level 193), though I have yet to pass Maple Warrior 30 and Sudden Raid 30.