1. Clean trucks with permanent, professional signs. Magnetic signs scream "I will take this sign off and run if I need to". Put some clean advertising on more than just a 12" x 24" sign on the door. Kinko's will take your design, and print it up on adhesive vinyl signs that you can attach yourself. MUCH cheaper than having some sign company do everything for you. Try to store the tools systematically, rather than dumped all over the logs & brush.
2. Uniforms on the employees, even if it is only matching t-shirts. Really cool if you can get your guys to wear hard hats with company logo's. Your customers will be fooled into thinking they are well trained professionals.
3. Business cards in every truck, in every employees hands, at all times. A person that inquires while you are on a jobsite is the best lead you will ever get: make a good impression!
Cheap business cards are a turn-off. Make sure that your card is neater, cleaner, and printed on better paper than your competition. People will notice. Make sure that the back side of the card has room to scribble in a bid.