Probably the biggest mistake new shoppers make is not being organized before they start.
You need a separate email account for your shopping rather than using your existing personal account. My shopper email account gets possibly 50-60 emails a day during parts of the month. Most of it is junk for jobs I wouldn't take because the fees are too low, the areas to be shopped are too distant or unsafe or they just won't fit my schedule. I strongly recommend setting up a gmail account with a legitimate sounding name just for shopping. You can sign up for it at mail.google.com and it gives you a large enough space you can save all your job related emails for years while the emails you trash get cleared out in about a month.
You need a paypal account that uses the email address you have set up for shopping. Many companies pay by paypal and you would prefer be paid that way for a whole lot of reasons. There is no cost if you just sign up for an individual account and it is easy enough to transfer payments from paypal to your bank account.
You need some sort of logical file system for handling your shops, notes and such, both before you go out and do the shops and for retaining notes and such after you report the shops.
All the skills you need to be a good office employee you need to be a shopper: computer skills, reliability, punctuality, people skills, follow up, organization, and writing skills.