To be an effective consultant, I would:
(1) start reading any documentation that (a)with the company (b)other consultants.
(2)go to a course on SAP HR Payroll – US. You will find on-line as well as class-room courses.
(3)forums such as this – would help in resolving smaller issues – the question you are asking would not be in this category .
Hope this helps.
The above said advice would be really helpful as well as i suggest you to get SAP installed in your home PC if you have and explore yourself on US payroll in each vertical i.e complete customizing and specially on Schemas, PCR’s, Reports and functional specifications.
Hope this will improve ur confidence level. and you can practice trial n error without a fear.
It would be good to get your hands dirty when you can. In other words, find opportunities to solve small issues first. Study whatever is available – requiremets, how it has been catered for in the design, how it is implemented, any issue log. Try making a change in the sand pit or dev client. Run the process – time eval, payroll or whatever is the area of issue – with log display. Study the log. Check where the problem is.
Even without an existing issue, play around in the sand pit client. See what is happening currently, then do a small change and see how it affects output.
But without full testing in the Dev/test client do not transport the changes to QA client. Without adequate user testing and their sign off do not risk putting the change to the prod client.
Any change should be adequately documented.