This really depends on your tastes and what you like. Most peoples ideas of a perfect garden are quite different. Someone may like certain trees and plants as part of their landscaped garden but for others they may be horrified at even considering planting the same trees and plants in theirs.
As everyone’s taste is different the best thing to do is to start with your own imagination. Now this is where professional landscapers have a head start because they have had many years of experience and have  drawn many designs (probably hundreds over the years) that they can quickly throw out ideas and run with the one their client gets excited about. However, there are things that you as an amateur or novice should be aware of to minimize the chances of a complete mess.
The first thing you have to remember is that there is no right or wrong garden and if you think your garden will be perfect in the style you enjoy then go for it because after all its your garden and you should put a bit of your personality into it.
Secondly, consider your budget and how far it will stretch. If the landscaping project cannot be completed in one go due to time constraints or a small budget, then its probably better to break it down into smaller mini projects so that it does not get overwhelming. Infact it may be even better to pick little projects that can be completed at weekends. This will keep your motivation up as you see progress being made towards the end result.
Thirdly, to help you along its best to invest in some good quality gardening tools. A good set of secateurs will make gardening easier and quicker. On the other hand cheap secateurs will damage plants and make the garden much more difficult to maintain thereby also increasing the time to do the job properly.
Fourthly, keep a watering can handy or (if its a really large garden) a hose. This is especially important in times of short rainfall in the summer months so choosing plants that suit your climate and soil conditions will minimize the risk of losing plantings.
Finally, create a small patch where you can pick fresh flowers to use inside your home. This will avoid you taking flowers from the designed areas in your garden and this will help to maintain its beauty and also allow you to enjoy the flowers from your garden.
Whatever you decide for your perfect garden its best to have some great ideas to get started with. Its probably a good idea to have a look at some landscaping or gardening magazines. Some of the home and garden magazines are also a good bet to give you ideas you can think about. Failing that you can also drive around your neighbourhood to get some ideas on front garden design.