Alternate Abilities are special abilities that characters can train in by diverting some or all of the experience points that they earn. It takes roughly the same amount of experience to earn one point of “AA” as it does to go from 0-100% of Level 51. Alternate Abilities allow you to “customize” your character by attaining new skills or improving old ones
People give different advice for when to stop levelling and start AA's. Indeed, some rangers like to do combined normal and AA XP together. I can only tell you what I did, which was wait until level 62 and switched to 100% AA XP to start gathering my AA's. The advantages to this is that you seem to get AA's quite quickly at level 62. The disadvantages are that you will not have any of your archery mastery AA's, which will make it harder to hunt alone.
A suggested starting template is:
Innate Run Speed - Rank 1, 2, 3 (3 pts) 3 pts total
Innate Regeneration - Rank 1, 2, 3 (3 pts) 6 pts total
Combat Fury - Rank 1 (2 pts) 8 pts total
Mental Clarity - Rank 1 (2 pts) 10 pts total
Natural Durability - Rank 1 (2 pts) 12 pts total
Combat Agility - Rank 1 (2 pts) 14 pts total
Natural Durability - Rank 2 (4 pts) 18 pts total
Endless Quiver (9 pts) 27 pts total
Archery Mastery - Rank 1, 2, 3 (18 pts) 45 pts total
Innate Camouflage (5 pts) 59 pts total
Ferocity - Rank 1, 2, 3 (9 pts) 54 pts total
Ambidexterity - Rank 1 (9 pts) OR Punishing Blade - Rank 1, 2, 3 (12 pts) 68 OR 71 pts total
Dependant upon whether you primarily use 1-hand or 2-hand weapons
Combat Stability – Rank 1 (2 pts) 70 OR 73 pts total
Physical Enhancement (5 pts) 75 OR 78 pts total
Click here for a link to EQOutrider that gives 3 different path suggestions for your AA's. Once for archer, melee and utility ranger
This link advises of the recent AA consolidations (eg there were so many of them, some have been combined)