An ERP project touches almost every part of a business, which is why much of what decides its success happens before anyone logs in to the new system. A little preparation gives the project clearer scope and fewer surprises.
Agree why you are doing this
Write down the business problems the project should solve, in plain language. "We cannot see stock across both warehouses" is a far more useful starting point than "we need a new system". These statements become the test for every scope decision that follows.
Name an owner for each process
Each major process needs someone from the business who can describe how it works today and make decisions about how it should work tomorrow. Those people will need time set aside, so plan for how their regular work will be covered.
Look at your data early
Customer lists, product records and opening balances all need to move to the new system. Reviewing them early shows how much cleaning is required, and duplicate or incomplete records are much easier to deal with before the migration than after it.
Decide what to standardise
Not every existing habit deserves to be rebuilt in new software. Ask whether each special case still serves a purpose. Using standard features where they fit makes the system simpler to learn and easier to upgrade.
Plan for people as well as software
Explain what is changing and why, involve the people who will use the system, and budget time for training. A system that is correctly configured but not adopted does not deliver what the business needs.