What ways would you recommend to improve one's immune system and general wellbeing if they are somewhat sickly, prone to colds, bronchial disorders, asthma, and ear infections for example? I am asking for a friend who has these issues so of course there might be other details necessary to know, but in general, it seems as if he is just of a weak constitution and he asked me how he can improve this.

I get asked this a lot and I always start out by explaining to people that the immune system is not a singular thing.  Instead it is a multitude of things such as the various white blood cells, various cytokines, various glands, various enzymes, peroxides, the flora, etc.  So there is no single way to boost the "immune system".

In general though the best things that can be done to support the immune system are to keep the adrenals up as well as flora levels.  To keep the adrenals up the most important nutrients are vitamin C and pantothenic acid, both which are best from natural sources.  Keeping stress to a minimum and avoiding stimulants and steroids will also help.  Adaptogenic herbs also build up the adrenals:

http://curezone.org/forums/fm.asp?i=1527351

You mentioned he is prone to asthma, which right there indicates a problem with the adrenals:

http://jamessloane.hubpages.com/hub/Alternative-Therapies-for-the-Treatment-o...

The vitamin C suggested for the adrenals will also support the thymus gland, considered the master gland of immunity and will help with white blood cell function.

The flora help to prevent pathogens from entering the body through the gut and produce immune stimulants among other functions.  The best way to build up the flora is with cultured foods such as kefir, miso, tempeh, etc. and with fiber sources to feed the flora.  The best fibers are "soft" fibers such as rice bran, oat bran, apple or pea fiber, FOS or inulin and vegetable gums (konjac, xanthan, guar, etc.).

I was wondering if there are things he can take every day over months, for example, herbs like andrographis, or certain foods like coconut oil or ACV, and other things that target lung health in general (he doesn't smoke or drink). He's 26 years old and generally in good shape otherwise.

The suggestions I gave above can be done long term as can coconut oil.  Andrographis I would reserve for infections and apple cider vinegar I would not recommend long term.  It is best to allow the body to produce and secrete its own stomach acid.

On the same subject he has an earache that has been around for 4 or 5 days, quite mild, and someone used a little garlic oil dropped into the ear which relieved it temporarily but it keeps creeping back. Any suggestions for this? We did go swimming a lot in a lake last week but I'm pretty sure his ear was hurting before the swimming, although I am sure it did not help.

There are a couple of possibilities.  One is that he has water trapped down inside his ear.  This can happen with swimming, especially if people use cotton swabs to try and get water out of their ears after swimming.  Often they just push wax over the water.  The other possibility is allergies, which again result from adrenal dysfunction.  And this is a common contributor to ear infections.  If it is from water then a few things that can be done include swabbing the ear with alcohol, using a bulb syringe to carefully try and suck the water out or if he has access to an ozone unit with a discharge tube he can blow the ozone in the ear under low pressure to dry out inside the ear and to fight any infection.  If allergy related then I posted ways of building the adrenals earlier.