I started a new game wanting to be a Arcane Archer.
My Sorcerer is now Level 4.
I have feats: Weapon Focus Longbow & Point Blank Shot.
But I need an Attack Base of 6. Currently only 3.
How do I get my Attack Base up?
What level Sorcerer do you need to be to make the switch?

The only way to gat a higher BAB (Base attack bonus) is to gain levels. DOn't confuse BAB with Attack Bonus. AB also includes ability cores, gear and magic.

BAB. e.g.

1/1 Fighter will get to BAB 6 in 6 lvls...: Progression = 1, 1, 1, 1, 1, 1, 1
3/4 Rogue will get to BAB 6 in 8 lvls ...: Progression= 0, 1, 1, 1, 0, 1, 1, 1
1/2 Sorc will get to BAB 6 in 12 lvls...: Progresion - 0, 1, 0, 1, 0, 1, 0, 1, etc

One reason to multiclas with ftr or any other 1/1 BAB class is to qualify for a prestige class earlier. Another reason to get 4 of a 1/1 class before lvl20 is that it wil give you an extra attack per round. (AA is a 1/1 BAB class tho so sorc12/aa8 =14 BAB. If you can increase that to 16 BAB you'll get an extra attack per round (APR)).

One very clever tactic for a sorc is to take a single lvl of cleric on a lvl with a feat and get divine might which adds your cha modifier to your damage. If you have good scrolls in your environment, divine power scrolls will also add a lot to your AB. The downside is you need power attack first and sorc has few enough feats already. But it is possible. I have a sorc26/AA13/cleric1 and she is deadly. Full power spells and an attack as good as a rogue with +20 to damage. Of course, most sorc don't have str 13. Maybe one for next time?

Have fun :)

Thanks for all the info.
I should have just kept going with my original sorcerer then.
And my new one probably should have been a Human or Half Elf, instead of an Elf.
But I find you can usually get through these games on Normal Hardness with a less than perfect build.