The answer to all these questions can be found in the World Wide Web Consortium and Mobile Top Level Domain Limited’s best practices guidelines for mobile websites:

THEMATIC CONSISTENCY - Ensure that content provided by accessing a URL yields a thematically coherent experience when accessed from different devices.

CAPABILITIES - Exploit device capabilities. Do not take a least common denominator approach. Work around Deficient Implementations

DEFICIENCIES - Take reasonable steps to work around deficient implementations.

TESTING - Carry out testing on actual devices as well as emulators.

URLs OF SITE ENTRY POINTS - Keep the URLs of site entry points short.

NAVIGATION BAR - Provide only minimal navigation at the top of the page.

BALANCED STRUCTURE - Take into account the trade-off between having too many links on a page and asking the user to follow too many links to reach what they are looking for.

NAVIGATION MECHANISM - Provide consistent navigation mechanisms.

ACCESS KEYS - Assign access keys to links in navigational menus and frequently accessed functionality.
Link Target Identification

LINK TARGET IDENTIFICATION - Clearly identify the target of each link.

LINK TARGET FORMAT - Note the target file's format unless you know the device supports it.

IMAGE MAPS - Do not use image maps unless you know the target client supports them effectively.

POP UPS -Do not cause pop-ups or other windows to appear and do not change the current window without informing the user.

AUTO REFRESH - Do not create periodically auto-refreshing pages, unless you have informed the user and provided a means of stopping it.

REDIRECTION - Do not use markup to redirect pages automatically. Instead, configure the server to perform redirects by means of HTTP 3xx codes.

EXTERNAL LINKED RESOURCES - Keep the number of externally linked resources to a minimum.

SUITABLE CONTENT - Ensure that content is suitable for use in a mobile context.

CLARITY AND CONTENT - Use clear and simple language and information concise

LIMIT CONTENT - Limit content to what the user has requested.

PAGE SIZES - Divide pages into usable but limited size portions.

PAGE SIZE LIMIT - Ensure that the overall size of page is appropriate to the memory limitations of the device.

SCROLLING - Limit scrolling to one direction, unless secondary scrolling cannot be avoided.

CENTRAL MEANING - Ensure that material that is central to the meaning of the page precedes material that is not.

GRAPHICS SPACING - Do not use graphics for spacing.

LARGE GRAPHICS - Do not use images that cannot be rendered by the device. Avoid large or high resolution images except where critical information would otherwise be lost.

USE OF COLOR - Ensure that information conveyed with color is also available without color.

COLOR CONTRAST - Ensure that foreground and background color combinations provide sufficient contrast.

BACKGROUND IMAGES -When using background images make sure that content remains readable on the device.

PAGE TITLE - Provide a short but descriptive page title.

STRUCTURE - Use features of the markup language to indicate logical document structure.

TABLES SUPPORT - Do not use tables unless the device is known to support them.

TABLES NESTED - Do not use nested tables.

TABLES LAYOUT - Do not use tables for layout.

TABLES ALTERNATIVES - Where possible, use an alternative to tabular presentation.
Non-Text Items

NON-TEXT ALTERNATIVES - Provide a text equivalent for every non-text element.

OBJECTS OR SCRIPT - Do not rely on embedded objects or script.

IMAGES SPECIFY SIZE - Specify the size of images in markup, if they have an intrinsic size.

IMAGES RESIZING - Resize images at the server, if they have an intrinsic size.
Valid Markup

VALID MARKUP - Create documents that validate to published formal grammars.

MEASURES - Do not use pixel measures and do not use absolute units in markup language attribute values and style sheet property values.

STYLE SHEETS USE - Use style sheets to control layout and presentation, unless the device is known not to support them.

STYLE SHEETS SUPPORT - Organize documents so that they may be read without style sheets.

STYLE SHEETS SIZE - Keep style sheets small.

MINIMIZE - Use terse, efficient markup.

CONTENT FORMAT SUPPORT - Send content in a format that is known to be supported by the device.

CONTENT FORMAT PREFERRED - Where possible, send content in a preferred format.

CHARACTER ENCODING SUPPORT - Ensure that content is encoded using a character encoding that is known to be supported by the target device.

CHARACTER ENCODING USE - Indicate in the response the character encoding being used.

ERROR MESSAGES - Provide informative error messages and a means of navigating away from an error message back to useful information.
Cookies

COOKIES - Do not rely on cookies being available.

CACHING - Provide caching information in HTTP responses.

FONTS - Do not rely on support of font related styling.

MINIMIZE KEYSTROKES - Keep the number of keystrokes to a minimum.

AVOID FREE TEXT - Avoid free text entry where possible.

PROVIDE DEFAULTS - Provide pre-selected default values where possible.

DEFAULT INPUT MODE - Specify a default text entry mode, language and/or input format, if the target device is known to support it.

TAB ORDER - Create a logical order through links, form controls and objects.
Labels

CONTROL LABELLING - Label all controls appropriately and explicitly associate labels with controls.

CONTROL POSITION - Position labels so they lay out properly in relation to the controls they refer to.