All the major online and private purchase photo editing programs (and smart phones) come with options for special effects such as selective colorization,  cross processing, color filter layers, and borders.  There is great debate about whether these effects add to or detract from images.  Generally speaking, it seems that hobbyists love them and pro's can't stand them. There are exceptions to that generalization of course. 

If you are working on a retro-themed blog then a polaroid or 70's effect can really come off well.  As a rule, it is ill-advised to edit the majority of your personal pictures with heavy hand though, that locks them permanently into a particular style.  (remember: always edit copies!)  Thick vignettes (that dark shadow frame) and orange or green color filters can lend an artsy feel but also leave your skin tones funky and tend to scream "Picnik!" to the rest of the world.  

If your project does benefit from a special effect or filter, then try to edit all the images for that project in a similar vein for consistency.  For instance, if you are making a photo book of your iphonography then using the same finish and filter for all the images will make the final album cohesive.  A good example of a photographer who rarely uses special effects but chose one style for a particular wall art project here. 

We have all played with special effects and I tend to be draw to interpretive photography vs literal myself.  Just passing along that if you google 'over-processed photography' you get an earful of opinions that may make you pause before you process. As Levar Burton used to say, don't take my word for it. 

iStock is a leading stock photography company.  You can check out their thoughts about filters and special effects here and here and here.  Selective color example here.  Common processing errors here. Comparisons here.

The standard processing 'error' list:

oversaturation (or under)

excessive color filtering

oversharpening (especially of eyes)

selective color

heavy grit 

fake lens flare

extreme angles/tilt of camera

As always, the best remedy is starting with good exposure.  The best exposure is usually nailed by manual settings.  Highly recommended that you work on that first if you have a dslr.  Then edit with a light hand. 

Recommended reading:

Understanding Exposure

Beyond Snapshots