Summary
A number of properties are provided to help in tuning the layout of the fields on your generated web page.
Controlling Properties
ScreenDef.ControlPositioning, ScreenDef.TopAdjustmentPx, ScreenDef.LeftAdjustmentPx, ScreenDef.CharHeightPx, ScreenDef.CharWidthPx, FieldMap.TableWidthOverride and FieldMap.TableHeightOverride
Details
Use the described properties to manage layout. Note that it is the PageTemplate that you select which will determine the look and feel, while these properties can help in alignment and so on.
Use the Web Preview Panel to check on your settings...but remember that when a web page is generated, both the ASPX and ASPX.cs files are ready to edit in Visual Studio for further refinement (in particular, moving and aligning fields from their initial positions on the screen as determined by these properties).