Read and understand the tender documentation carefully to get a full understanding of what the buying organisation is looking for. This will help you understand their criteria and whether you can meet all of them. If you cannot, develop a strategy to fill those gaps so that you can compete for the next tender.
 

If possible, visit the site beforehand to make your cleaning tender more specific and relevant - picking up on nuances or details your competition may not have spotted.
 

Provide assurance on how you will achieve consistent, outstanding cleaning over the course of a contract. Think about your processes for quality control, i.e., monitoring and checking your services.  Do these need improvement before you tender? What are your remediation processes if there is a problem?
 

Provide as much evidence as possible on previous experience, including accurate management information on how well you have cleaned in the past and monthly reports on meeting the Service Level Agreement (SLA).
 

Demonstrate your commitment to a sustainable future, such as by using the right consumables, having robust environmental policies and procedures, and calculating your carbon footprint or water consumption used for window cleaning. Consider how this commitment will help the buying organisation with their own environmental program.
 

Have all the necessary accreditations, qualifications, policies, and procedures in place to show that you have established a solid business foundation upon which you can deliver the required cleaning services. Ensure that your cleaning staff have the correct training and follow procedures. Have training certificates and use a matrix to control staff training.
 

If you're a small business or an SME consider focusing on the evidence you can provide that a smaller, local service is better than a 'big player'.  Support this with data and customer testimonials if possible.