1. My advice would be to start smaller jobs like walkways first (no vehicular traffic). Do not try a driveway, large patio, or raised patio. There is quite a learning curve to this type of work.
2. Beware of critical walls that retain a huge mass of soil and have water issues. Garden walls under 4' are a great place to start.
3. Be honest with people. Tell them you are certified but your experience is limited, and give them a 10% discount. Look for understanding customers who realize you might be slower but want to do a quality job. Some people are willing to wait for quality. These people turn into your favorite advertisers in my case, because "they were with you in the beginning."
4. Get good compaction! Rent the recommended compactor for your soils and use it!
5. Stay away from stairs for awhile. They are more complex and are basically mini, raised patios which bring up all kinds of new issues.
6. Use the best materials at first that are easy to work with. Stay away from big box store brick or really complex designs like flagstone imitation products. I like belgard products like dublin cobble modular since the laying time, and bond lines are short, and they still have a desirable look.
7. Use geotextile always and forever. Its cheap insurance.
8. Focus on your staging, timing of materials, and site setup. More time is wasted early on from not thinking about where to place materials and how to efficiently move it to where its needed.
9. Build a solid contract first. You will need clauses for overdig, hidden objects in the soil, acts of god, weather delays, efflorescence, etc.
10. Price by the job only and realize you may miss your mark quite a few times the first year or two. Mowing is a far cry from landscape construction. Try to sit down and plan out every move or action: excavate, haul, compact, fabric, base, compact,screed, measure, install sand, screed, carry brick, lay brick, cut brick, sweep, compact, sand, wet, clean up, reseed, plantings, etc. Remember 1 hour of planning in the office chair saves 8 hours lost in the field.
-Chris