Before migrating anything, it pays to decide what each application deserves. Gartner's TIME model does this with two scores: business value and technical fit.
The four places
Applications with high value and good technical fit are ones to invest in. High value on a weak technical base means migrate. Sound technology with little value means tolerate: keep it running at minimum cost. Low on both means eliminate.
Scoring
Score business value on criteria such as criticality, number of users and how unique the capability is to your business. Score technical fit on vendor support, security and compliance, cost to run and how well it integrates through APIs. Averages of one to five are enough to place most applications.
From place to route
The place sets the direction; the route comes from AWS's seven migration strategies: retire, retain, rehost, relocate, repurchase, replatform and refactor. For large portfolios, AWS's guidance is to rehost, relocate or replatform first and refactor once in the cloud, because refactoring during migration is the most complex route.
Waves
Applications that share data or integrations move together, or are decoupled first. Group them into waves by dependency and risk, start with low-risk applications to prove the landing zone and runbooks, then move the valuable ones.