how to define and save standard jobs and assign standard rates for the same job?

Are these jobs roles that have an hourly rate or are they pieces of your project that you bill for a fixed amount?  

There are two types of jobs, one which are dependent on project and the other one are independent jobs. Some jobs have fixed billing and some jobs are billed on hourly basis. We have such type of jobs as we are a Tax consultant firm.

For the hourly rates, you can associate rates with job titles and any user with that job title will automatically pick up the rate.  This can also be configured on a project by project basis.

As for the fixed billing amounts, these can be baked right into your project or milestone templates using the "Fixed Price" field.