While a lot of clients I meet have tried designing and building their own landscapes with limited reward thats no reason not to try yourself so here are some thoughts that might assist if its the DIY path you want to go down. First and foremost is to make sure you have a plan and by this I don't mean an idea in your head but something down on paper that's approximately drawn to scale. This is important for many reasons but in particular because 1) It will ensure you've considered your full brief from the start and can tackle it in an intelligent order and 2) It will make you consider what's happening beyond the edges of where the work stops. The reason this is so important is because there might be future goals ( think pool, driveway, carport, fencing, rainwater tanks ) that could make your current project redundant. Once you have your plan, mark it out ( chalk lines, paint or just use the hose) and then sit in and walk around it at various times of the day to make sure it works