If you're a first time business proposal writer, or a first time sales proposal writer, here's the question to which you want an answer - "Is there an easy way to do this?" My response? There isn't an easy way; however, there are easier ways.
If I were starting today I'd ask someone in the same size of business, who's had to develop winning proposals to build that business, to give me some advice.
Practical, hands on, there's nothing like sound mentorship to guide you.
It's the classic story of finding someone who is successful and modeling what they've done.
You can use the search engines and look for good content on the Internet, hopefully at a price you can afford.
It's there.
You just have to find it.
You could also hire a business proposal writer to do it for you.
But if you want to do it yourself, you want to understand the process, and you want to see how long it's going to take, let me be your navigator.
Essentially I want to provide you with a format to follow.
Now I'm not discussing writing per se, I'm talking content.
I'm putting you in the shoes of your client.
What does your client want to see? I suggest that there are seven steps a first time business proposal writer, or sales proposal writer needs to cover and the sequence in which to do them.
They are:

1. Show the client that you understand the situation
What does the client want to achieve? What is the present situation? Prove to the client that you understand what is going on here.

2. Figure out what research and analysis you must do
Explain that you have to discover how to get the client from the present situation to the desired situation.
Do you need to do a survey? Do you need to talk to suppliers? Do you need to talk to customers? What input from client staff might you need? What industry trends might be important? And having carried out that research, the analysis that might be required and how that might affect your work.

3. Your USP - your Unique Selling Proposition
This is all about how you intend to resolve the situation and some idea of its execution.
It may be your specific skills, your great idea, your experience, your qualified people.
Where you can, provide a case study of a project you've successfully completed that may be similar to the requested proposal.
If you have appropriate testimonials or endorsements, add those in.

4. Background information about your organization and its people
Tell the client about your organization and the people associated with it, what their qualifications are and their successes.
Do the same for any subcontractors you plan to use.

5. Logistics - includes budget, responsibilities and deliverables
Provide a budget for the client, details on what you will be responsible for (include what you expect the client to be responsible for) and then set out deliverables - what will be done by when and by whom
6. Executive summary
Many clients only want an executive summary.
This pulls the proposal together, summarizing the salient points from the above sections.
It may be enough for the client to make a decision
7. Cover letter
The cover letter goes with the package to the client.
If it's a brief proposal it may serve as an executive summary.
The cover letter thanks the client for the opportunity, may summarize key points in the proposal, as well as suggest next steps.

Depending on the proposal request, the above steps may require several pages each, or they may simply require a one or two page letter.
It depends on the scope of the proposal.
Here are a couple of other key points to bear in mind:

1. Know who your audience is
You want to communicate effectively to your audience.
Smaller companies are likely to be receptive to a more conversational style of writing (which I prefer).

2. Know who the decision maker is
This is an important one.
I've submitted proposals to those I thought were making the decision - they even said so themselves.
Be cautious.
That assumption can turn out to be invalid.
Make sure you know who says yes to the project.

Working up a business proposal or a sales proposal, and being new at it, is a challenge.
My intention is to give you some straightforward ideas as well as a format approach that a first time business proposal writer can easily follow.