How To Start A Model
A good start to any model will help increase your quality and modeling speed, in the long run. This tutorial walks you through the my workflow for starting a modeling.
Don't Bite Off More Than You Can Chew
If you know you're not ready to, or just don't have the time to, don't model it. And sometimes you may not have the software to do it. If you want to do a hyper-realistic water effect, unless you have a program like Realflow, making hyper-realistic water can be a pain and hard to do (somewhat impossible).
Give yourself a deadline. Not only is this good practice, but it keeps things organized. Deadlines should be set by how complex the model(s) is. For a simple model, like a computer, a 1 to 2 day deadline should be more than efficient, to have it modeled, UV mapped and textured. This assumes that you can put at least 2 hours of work on it a day. For a complex model, like a car, set aside a week. Always assume it's going to take longer than you think it's going to take. Also, don't forget to factor in rendering. If you're making the entire scene, render time will start taking longer than a couple minutes so this should be factored in as well.
Know What You're Modeling
Let's say you're modeling a car's suspension. Before you do any modeling, drop by wikipedia or howstuffworks and find out how a suspension works. A mechanical knowledge of whatever you're modeling will help make the modeling time go faster, also, more accurate. For something not as generic as a suspension, try using a patent search. You can normally get the patent number off the website that makes the product that you're modeling.
There's no better place to get great reference of anything than Google image search.
Choose Your Geometry
Before you start modeling, you need to decide what geometry you'll be using: NURBs or polygons. NURB surfaces are based on NURB curves. NURBs are best for modeling solid objects like television remotes, cars, or any solid mechanical object. Some people have had success modeling objects like human heads or full bodies using NURBs. I don't recommend NURBs for that use, due to you're limited so much by the surface direction and your model will be made up of different pieces.
If your scene's going to have more than a couple of models in it, it's good to create a new project and keep all files related to that project in that project. For more on projects, read this tutorial.
If you opt to use polygons, it's best to estimate what your poly count is going to be. If you have multiple objects, keeping poly count in mind will help prevent memory issues later on.