Is there any way to automatically evaluate an input cell after evaluating the previous one without the need to press ENTER?
One way to acheive this is:
a = 1 + 2 If[a == 3, SelectionMove[EvaluationNotebook, Next, Cell]]; SelectionEvaluate[EvaluationNotebook];
Other way is by adding
CellTag to our "conditional" cell. Use Crtl+J on that cell or use menu: Cell > Cell Tags > Add/Remove... to add tag, here I used
a = 1 + 2; If[a == 3, NotebookLocate["only if"]; SelectionEvaluate[EvaluationNotebook] ]
This seems to be more bulletproof.