You need documentation for your work history. The more the better. Payslips and bank account receipts go a long way. Make sure you cover the whole work period. Tax returns are also good. More evidence is better.
If you give the wrong phone number, even by one digit, the number is useless. Accuracy on immigration forms is like that. The departments looking at these forms will pick up on these problems, and slow down the process to ask questions.
It can be a problem when you tick boxes on a form and find you don’t fit into a certain category, or fit into two at once! This will not disqualify you, but it will possibly slow the application down as they sort out the inconsistency.
You will tick a certain box for your type of employment. Make sure your (former) employer tick the same box, not the other box that looks similar.
The people who read your forms don’t know your personal history in advance. Make it as easy on them as possible, and keep is chronological. Have digital files labelled accordingly as ‘passport’, birth certificate’ …etc.
The immigration will look as Facebook and other online sources. Make sure there is nothing compromising there, or anything that appears inconsistent with other information.
Submit everything for applications on time.
Only use a registered Migration Agent, Sydney has many. There are many scams in immigration, but a registered agent can be of legitimate benefit.