Use the format text tool. It looks like a paint brush. Click the field to copy the format of, then click the paint brush and then click to field to paste the formatting on.
For many fields, click the field to copy then control click the paintbrush then click multiple fields or select them while this tool is activated.
Or, with nothing selected, set the text size, font style, color, etc and it will become the default for any future field.
Thanks detatango! I read you can double click it, too. Then click multiple fields.