Experience here has been a lot different than Rich's though I have no doubt thats a daily occurrence for many. The range in "commercial work" is so wide you could be speaking to anything from a small strip mall or single story commercial project with 5 or 50 boxes run by a design/build GC working with the owner or you could be talking full on Architects, interior people, huge drawing sets and so on. Landing on a disaster in either situation is just a roll of the dice but the alternative is a nice job.
We are a small shop and bust our butts (i.e. probably work a lot harder to complete) than most and provide a LOT more interaction than any of our contractors are accustomed to. That doesnt neccessarily equate to miles more work. But being in the process seems to help a lot and with regards to the contractors your dealing with, for me it gets you in and around their world and you will quickly get a feel for the ones to avoid.
We are lucky in that in our area there are not a ton of options so I have a direct and open conversation with any contractor that we simply cant be their bank. We have a few that will push us with regards to deposits stating that they can order $$$$ worth of xyz and not be invoiced til it lands on the job and have 30 day terms. I make it clear to them that thats all well and good but I simply cant do that and just like they receive deposit on the start of the job we require that as well and if that not acceptable they have to look elsewhere. Thankfully every single contractor we've dealt with other than one are more than willing to incorporate deposit into the job, payment of all but 10% on delivery of the material, and zero of them have held the 10% until job completion, they have all paid the 10% within 30 days of final delivery.
Maybe we are lucky, maybe its because of the open dialogue, maybe its the service and interaction, or a combination, who knows.
With regards to reading drawings, if thats a short-fall in your skills you would be best to look into some classes or education on plan reading as its a MASSIVE part of the process and in my experience you will be expected to be able to read/review the drawings in detail, find and identify all of your scope in the project, outline that scope in detail as Alan states, and then it had better fit. There is the opportunity to have a little bit of back and forth with the contractor/architect but I dont think you will get very far if they pick up straight away that you have no comprehension of the plans. You may find a contractor that will get you rolling on smaller projects and spend some time with you helping you understand the plans a bit, who knows.
There is a decent book called Blueprint Reading, Construction Drawings for the building trade and no doubt a ton of others which may be a good start. Getting into a good 3D CAM software as well where you can import .dxf's of the prints and highlight/markup your scope right on the plans in the computer can be very handy and doing the work of fairly quickly 3D modeling the space around your work can really help you get your head around the drawings quickly.
The approach we take on a small scale is to protect ourselves, and dont undervalue what you provide. Dont be afraid to say, this is what I can offer, and this is what I need. They will either accept or walk away but dont budge. As many have said, its not worth the risk, a single non-payer or slow payer, will cripple a small shop. So make sure your arrangement gets you covered out of the gate and anything left hanging is money that wont destroy you to wait on or never see (which hopefully never happens).
Ive never looked but I would imagine there are miles of webinars, youtube videos, on-line courses, and so on, with regards to plan reading. Hit the bookstore, library, amazon, and get sharpened up, and ask a couple of your builders for some past projects to work up and bid as practice. I'd bet if they see your eager youll get a lot more help from them than you'd think.