Agile planning looks different, but planning must be done. Often. Some general rules of thumb include, keeping options open until the last responsible moment, focussing on adapting and replanning rather than on conforming to a plan, and favoring smaller and more frequent releases.
The Backlog
Similar to to a work breakdown structure (WBS), the backlog contains all the issues, or tasks, currently expected to be done in a project. It also contains work that might be done. Therefore, a backlog is the list of issues which are not yet committed to in the current work cycle, or iteration. The product owner, with help from the customers and team, will manage this long list of issues by ordering, prioritization, and roadmapping the work. Theoretically, anyone can add a task to the backlog. That, of course, does not mean the team has committed to doing the work.
Ordering and Prioritizing
To prioritize a list means to order its items by their importance relative to each other. The product backlog is not guaranteed to represent an ordering of items/tasks by either value or priority. Yes, in general items will be ordered by priority, or value, but that is not always the right order to maximize return on investment (ROI) or to create the most value for the business or customers. The product owner,with the help of the the team, must consider the entire backlog when ordering and prioritizing work.
Estimating
Backlog items must be estimated prior to sprint planning. There is a balance between not estimating and spending too much time estimating before enough information is known to create useful estimates. In general, items near the top of the backlog need to be fully broken down and estimated for sprint planning to be effective. How far into the backlog should this work be done? It depends! How far ahead must you be able to plan in detail? Learn more about estimation techniques on the estimation page.
Iterations (Sprints)
An iteration is a timeboxed work cycle and the order of each item in the backlog affects when the item will be pulled into an iteration (sprint) and committed to being done. Iterations are grouped together to create product releases and are an important tool in planning your product roadmap.
Releases and the Roadmap
What constitutes a release and how do releases help you build a product roadmap? Think of a release as a packaged product, a separately delivered product component, or a special pack of added features being delivered at once. When thinking about releases and how they help you build a product roadmap, ask yourself: what are we doing, why are we doing it, and how does it tie back to our goals and objectives? With this information, you should be able to decide what to work on on now (currently), what to work on soon (near term), and what you will work on in the future.