f you have just done lots of activity and your blood glucose is low, then you need would need fast energy... simple sugar is very effective in this case BUT People with diabetes have the opposite problem, too often their blood glucose is high, so they wouldn't normally eat sugar by itself. The same goes for products containing a lot of sugar ( which are also often combined with a lot of sat fat) , products such as cakes, pastries, biscuits , chocolate bars etc.
Better carbs are those that are in foods that are high in vitamins,minerals and fibre.
Vegetables, fruits, dairy produce,pulses and cereals contain varying amounts of carbs.Eating a wide variety helps ensure a good mix of nutrients.
All carbs will raise your lood glucose levels, but some will do it more quickly than others, if they are absorbed slowly your body will have time to deal with them causing a lower rise in blood glucose levels. Many carb containing foods have been tested and ranked, the ones that act slowest have a low number, those that are fast a higher number (pure glucose is 100) This is the glycemic index. Sometimes the results are very different to what one would guess and different varieties of the same food have very different gis.(eg some rice has a gi of almost 100 where other varieties are half that)
Many people use t the gi index, coupled with their own meter to select the best foods for them . Portion size needs to be taken account, a large portion of a low gi starch will still raise blood glucose high.
People have also lost weight and controlled blood glucose levels very sucessfully using the GI. The glycemic index website is a source of lots of information about it,
Others have also mentioned using diet books . One often mentioned being really effective is by Ricky Gallop, Another diet that has been recommended on here is by Nigel Denby, the link below is to a book about the Glycemic load diet, this incorporates portion size. The amazon page lets you look at the first few pages which explains it well,
info on the glycemic index
http://www.glycemicindex.com/
Gallop Gi diet
http://www.gidiet.com/en-gb/faq.php
GL diet
http://www.amazon.co.uk/GL-Diet-Nigel-Denby/dp/1844541126