Since I've done quite a lot of painting furniture for a distressed look, I thought I'd share my experiences with anyone wishing to do so themselves. It was trial and error for me, since there are so many methods out there. Also, after spending literally hours searching e-Bay for those little extras that make all the difference to your furniture, I can refer you to a couple of links to find sellers I discovered recently.
You can just paint one coat of gloss sparingly over an item, deliberately leaving it lightly painted, so that any carved details show up better. Some designers actually advise you to batter your furniture first with a heavy item, to add random distress to it.
If the item is old, you don't need to paint it with primer; I personally just sand the edges down first. Just one or two coats, depending on the look you wish to acheive, with gloss (Not high shine gloss!) and when it's dry, sand or scrape the edges randomly with a sharp tool such as a flat-ended screwdriver, and/or chip a small layer of the dried gloss right off at random places. If you are going to paint several items together, you need to set aside a few days, both for drying time and for the upheaval it may cause. Best do it outside in summer, though! (If you're doing it indoors, make sure the room is well ventilated or you might get a bit hyper on the fumes.) In between coats, I wrap cling film around my brushes to save having to wash them, since leaving them out renders them useless.
N.B: If you do want to prime furniture first, I would advise you to buy the real deal like a good undercoat and don't be tempted to cut corners by using a cheap emulsion, for example. The end result is that your furniture blisters. Not pretty.
Another tip: Invest in a decent set of brushes. There is nothing more soul-destroying than to find your newly-painted furniture has the odd bristle dried into it. Especially if that furniture is used for anything concerning food. Euw.
Modern, MDF furniture can be painted too, and opinions differ as to whether primer should be used as undercoat first. It depends on the shade it is and the shade you want to come through after you've distressed it. If it's a beech shade, you could use dark brown primer first, then paint it the shade you want such as antique white, so that when you scrape or sand the edges down, the dark brown comes through. I did this with a relatively newish, gaudy display cabinet that was fake mahogany. It was really dated, but it had been given to me as a well-intended present so I decided to paint it antique white. I bought a pack of four plaster embellishments here on e-Bay and stuck them on the corners of the unit. I did a similar thing on my fire surround, by adding a unique mould for that classic Country Home look.
If you're feeling particularly crafty, you could buy some material to re-upholster an old chair. All you need is a good staple gun, fabric glue; in some cases, upholstery pins, and a steady hand. I painted a chair distressed-style, pastel blue, let it dry and then covered it in blue toile, using fabric glue to stick a lilac lace trim around all the edges. I painted a modern Monks chest white and covered the seat and back in the same blue toile. (I use the storage part to hide the ironing in. I detest ironing.) Toile fabric has been used to upholster furniture for years and is really in at the moment. But make sure you buy your material from the upholstery or curtain section if you want it to last. http://shop.ebay.co.uk/i.html?_nkw=plaster+moulds&_sacat=0&_trksid=p3286.m270.l1311&_dmpt=UK_Crafts_Ceramic_PotteryMaking_SM&_odkw=plaster+embellishments+moulds&_osacat=0&bkBtn=
For upholstery pins to finish a newly-upholstered chair or sofa, see link: http://shop.ebay.co.uk/i.html?_nkw=upholstery+pins&_sacat=0&_trksid=m270&_odkw=upholstery+pins&_osacat=0&bkBtn=
Toile fabric for Shabby-Chic: http://shop.ebay.co.uk/i.html?_nkw=toile+fabric&_sacat=0&_trksid=p3286.m270.l1313&_odkw=Armoire&_osacat=353&bkBtn=