There's loads of advice online for blocking and making blocking boards; my method is very simple indeed. I use the interconnecting foam mats from the ELC, though keep an eye out, often Wilkinsons or Tescos sell these cheaper, and I have a hair dryer, pins and silicon paper too.
The hair dryer is for when I use laundry spray starch, in order for that stuff to stiffen fabric it needs heat, I've found using a hair dryer works great, though for small flat crochet you could pin to an ironing board and iron, but you do have to be careful not damage the yarn. I use a blow heater for sculpting flowers into the desired shape. This is how I shaped these snow drops:
I sprayed the flower, and with the fan blowing, I gently pulled the petals into the shape I wanted and kept the heat on the petals until they were dry. This is also meant they hanged better when added to the spring garland.
Pins, buy lots, when it comes to pinning out items, more is preferable. And if blocking circular items, it an be useful to print off circle guides, just be careful the printer ink doesn't transfer to your crochet. I tend to cover with cling film, or a piece of silicon paper and then pin the item onto that.
If I want to stiffen an item as well as block it, my most go to stiffener is pva glue diluted 50/50 with water, or less for really stiff items. The main issue with pva glue stiffener, is it can yellow quite quickly (items needs to be out of sunlight) and it can sometimes change the sheen and colour of yarn, so testing on a small area on the back of an item is a good idea! For my garlands, I usually just brush the pva/water solution onto the back of my motifs, this solves any colour changing issues.
|Autumn Owl Garland blocking using pva glue|
Although another advantage of glue stiffener, is you can glitter to your items if you wish - I often add iridescent snowflake glitter to the snowflakes I hook.
Sometimes, I want items to be super stiff, and this is where the entire piece gets dipped in the solution and then gently wrung out (if you end up with flakes after drying, there was too much stiffener on the item). The glue stiffener is perfectly adequate, simply add less water, but of course it does have its limitations. Other stiffeners include sugar water; 2 parts sugar to 1 part water and boiled until the sugar is dissolved, then left to cool. Do be careful, sugar burns are horrific. Sugar stiffener is good for items you want to be a touch sparkly - so snowflakes and the like.
There's starch stiffener, very good for achieving superb stiffness, (clean minds only please :P), you need laundry powdered starch, or a cheap alternative is corn flour, 1tbsp of cornflour to 1/2 cup of water and simmered until clear and thick. Let cool before using, as it will be very, very hot. Keep any left over starch in the fridge.
Oh, and next time you have a takeaway and get given those plastic takeaway tubs, keep them, great for reusing for stiffening, add solution, after cleaning of course, I don't recommend chinese takeaway starch. Once solution is added, simply lay the item in the starch, and then lift out and gently squeeze out excess.
And recently I came across using Epsom Salts as a stiffener, I've not tried this yet, from what I gather its adding espom salts to hot water until they no longer dissolve, leave to cool, and then dip items in the solution, wring out the excess and pin out (or shape around an object for say bowls, or balloons for spheres). It's suppose to leave the yarn sparkly.
I use the silicon paper, mentioned above, when I'm using stiffening agents, as it stops the fabric being stiffened, sticking to the foam mats.
For bog standard blocking, I just pin out the item on the foam mats and then spray with water and leave to dry - if I'm in a hurry I'll use the hair dryer to speed things along.
You can use steam from an iron, but you do need to be careful, pure wool can shrink or burn, and acrylic can melt - so it is vitally important not to let the iron touch your work. I find steam is the most effective for blocking acrylic, and for cheaper acrylics, can help to soften the fibres. I don't actually own an iron though, so I tend to use my steamer, it's a bit cumbersome, I have considered purchasing a small handheld one, as I have a natural aversion to irons.