If you work in Japan they should have a バイト警護 guide. If not, then I highly recommend you watch/read 日本人の知らない日本語. You will learn some really interesting stuff from that.
If you can read Japanese, try reading a Japanese resource about how to use Keigo. It’s useful to see it from a native perspective and I found it helpful myself.
Because even Japanese people get keigo wrong, there should be dozens of resources in both English and Japanese out there to use. Admittedly, I’ve found many of the English resources lacking because they simply state the forms but don’t go into the details of which accompanying vocabulary gives the best impression. If you feel your Japanese reading is good enough, it might be best to foray into learning this learning from using resources targeted toward Japanese native speakers because they’re more robust with explaining the do’s and don’t’s.
With that being said, what kind of interactions are hoping to have with your customers? If you’re aiming to engage in friendly chit-chat, etc. です-ます with adding ご or お to nouns pertaining to the customer should suffice. Handling business affairs with customers can be a little dicey due to the higher expectations required. I would suggest not only researching the forms but work with a native (if possible) to help you polish your delivery.
日本語の森 has a video series that explains honorific, humble, and polite speech using explanations and skits. They have a series called “JLPT N2 試験によく出る文法 #1/12” (the link is to the first video). Although do okay with explaining things, there’s a lot more to learn with understanding the common pitfalls speakers often fall into such as being overly polite (二重敬語) or forgetting who the grammatical subject is in the forest of causative verbs coupled with giving and receiving verbs, so dive into as many resources as you can.
My quick tips are to: remember that there is a difference between humble keigo (used when talking about one’s own actions or state) and honorific keigo (talking about another person), and try to learn matching sets of the same base verb; keigo is not as uniquely Japanese as some sources like to make it seem (think of “how can I help you?” Versus “how may I assist you?”); take a deep breath, and realize that as a non-Japanese person not in a role that requires strict adherence to keigo, any attempt to be polite will probably be very well-received
Yeah, I get the impression that a lot of non-natives aren’t aware that verbs aren’t the only part of keigo. There are many, many special expressions and nouns that you have to use in order to use “proper” keigo, and thus your keigo will just sound half-assed or odd if you toss in the normal nouns and expressions you know alongside the fancy verbs.