You might be aware of this information, but anyway........
Have you got the rear mech range limit screws set up incorrectly.
The mech should be able to shift by pressing it with your hand in to lowest gear. (maybe with the cable disconected or loosened). When you let go with your hand it should go in to highest gear on the spring pressure alone. If you can not obtain 1 first gear adjust the "low" or "L" screw on the mech, if not highest gog engaged alter the LOW or L screw.
Once these limits are correctly set it should be a matter of pulling enough cable tension thorugh to allow 1st gear to be selected and then the adjustments on the cable adjuster screw should address the indexing isuses.