use a debit or credit card to pay for everything (that way you don't have to keep reciepts). Anything over 12 dollars is a 100 percent right off, Talk to your account all the time. For 2010 my account called me and I couldn't put any checks in and had to run my account down(all of nov-dec 31) Without that relationship I would be screwed. And like cactus said "s" corp.. winner winner chicken dinner!
I've tried Quickbooks and didn't care for it, last year picked up the Sage Peachtree and really like it, takes some getting used to though. Simplifies everything as far as invoicing, billing, money in, tracking payment you make to suppliers, insurance etc., but I basically use mine for invoices, keeping track of what is coming in, jobs.
I keep all of my receipts. I have a file folder marked for the current year, pile receipts in my wallet then put them in the checkbook and file receipts in folder. I have a business account for everything I buy. Spent Saturday going thru receipts seperating truck maintenance, welder maint., diesel, welder gas, meals/travel exp., supplies etc. Stapled sticky notes on each marked what it was with the total of all receipts in that group. Now I know exactly what I spent on what, Airgas, other welding supply house I go to, steel guy, decorative steel folks and so on.
As far as diesel fuel and truck maintenance from what I've learned you have two options. (A) Write off your fuel and maintenance, i.e., oil changes, repairs or option (B) Write off your mileage. Seems with the mileage I drive it is always better to write off my mileage. I think it's something like .58 cent's per mile is what you get.
If you have a home office, your allowed to write off a certain % of that. I write off my cell phone bill, at least part of it, we have a family plan so obviously can't write all of it off. Work clothes, work boots, shirts etc., write off. Although one year I told the accountant what I spent on work clothes at the Goodwill, Thrift stores and she asked me if I had uniforms, told her ahhhhh, what?? Told her I wear cotton blue jeans, cotton shirts that I buy specifically for welding/working. She wouldn't allow it because it was not "uniform company" uniforms. Told her I spend $36 on a shirt that will get burnt, dirty, holy and whatever else that happens and she still denied me. The next year I just slid that into my expenses without specifying "uniforms".
Like Cactus said, find an accountant that if familiar with what we do. Kinda like the insurance agents, finding one that understands what we do off our trucks, what we work on.