1000mcg 1-2 times per week is a good therapeutic dosage for people who aren't B12 deficient.
Less is more when it comes to vit B12 injections. Although B-vitamins are water soluble vitamins and can not lead to toxicity issues when taken orally - that is NOT the case when it comes to injections. The injections can lead to toxicity issues if too high of a dosage is used.