What are the early signs of a Urinary Tract Infection?

Is there a way you can tell if one is coming before the actual symptoms?

The color of urine changes.
you have burning sensation.
difficulty in urinating.
frequent visits to bath room.
If you have any of these signs, right away drink lot of water and lot of cranberry juice. if you don't like juice then get the tablet from drug store. It works most of the times.
If it does not cure in 1 day go to doctor.

Urinary Tract Infections are caused by different organisms. E.coli is the most common pathogen. The organisms enter the urinary tract through the ascending urethra. Bacteria then inhabit the distal urethra and external genitalia. Organisms enter the urethral meatus and travel up the inner mucosal lining to the bladder.
Inadequate hand washing, failure to wipe front to back after voiding or defecating, and/or frequent sexual intercourse predispose women to infection.
Lower UTIs will cause pain or burning during urination as urine flows over inflamed tissues. Fever, chills, malaise (lethargy), nausea, and vomiting occur as the infection worsens.
Irritated bladder causes a frequent and urgent sensation to void. Irritation to the bladder and urethral mucosa will result in blood tinged urine. urine will appear concentrated and cloudy because of the presence of RBCs or bacteria.
If the infection spreads to the upper urinary tract (kidneys) clients will experience flank pain (low back), tenderness, fever, and chills.

Just some general info. Hope this helps answer your question!

Symptoms of UTI include difficulty urinating or painful urination, fever, abdominal and/or flank pain, and foul smelling urine. Not all of these symptoms may necessarily be present, though.

You won't be able to predict an infection, although I suppose one could be well tuned to their body so that they pick up on subtle stuff earlier than everybody else would notice.

No. They're very common though. To detect if you have one all you have to do is pee in a cup and the doctor will test the urine on the spot and if you have one you will get to go on some antibiotics.

If you leave it too long it could become more serious.