Bandleaders will almost always hire those side musicians who are organized and dependable- the ones who remember their gigs and always show up on time. Nothing is more embarrassing than having to explain to a client why a member of your band is running late. The whole band looks unprofessional, and gigs are tough enough to come by without that type of unnecessary drama.
The number one rule of gigging should be to write everything down immediately. If someone calls you to do a gig, don’t trust yourself to remember to write it down later. Do it right away.
Another great thing to do is to keep your schedule on a cloud-based application such as Google Calendar. For one thing, your calendar will be accessible from any computer or smart phone, and it will be safe even if your phone gets lost or broken. Another reason is that you can share your calendar with bandmates and they will be able to tell at a glance whether you are available to do a gig.
The last thing I’d like to mention is that you should always write down gigs that haven’t been confirmed. If someone calls to ask if you are available for a date, but the gig isn’t definite, write it in your calendar with a question mark next to it. Busy bandleaders have a tendency to forget to call you back an confirm gigs. If you have it written in your calendar, you can call back later to ask if it is confirmed. You can also check with the bandleader first if someone else wants to hire you for the same date. Either way, you end up looking like a prince.