That is a GIANT question.
There are a few threads here on Marketo without CRM. Things to consider:
- Workflow and funnel design steps
- Scoring Model
- Alerting Sales
- Data you want to collect
- Data Normalization/Standards
- Page and Email Templates
- Lead Lifecycle and RCM Setup (basic or full blown?)
- Are you connecting to a Product or other DB through API? How should that work?
- Fields you need vs. Standard Marketo Fields
Very long list of possibilities here. Please take a look here: Marketing Rockstar's Guide to Marketo - How to Use Marketo as well as topics at Etumos, RevEngine Marketing, Perkuto, TPG, etc before you begin building.