Problem 1. Identify the language
I found this diagram (in Russian). It seems to be pretty simple, and it amazingly covers a vast majority of world's languages. I took my liberty to adjust it slightly.

Note: this diagram does not pretend to be scientific at all. Its only goal is to let a beginner to quickly identify the script and, possibly, a language.
Problem 2. Identify the characters
Once you have recognized the language/script, you would probably need to identify the characters within the text. Some characters can be difficult to recognize.
For example, in Thai language (your text is in Thai; see below), the characters ง
, ว
, า
, and อ
, being hand-written, may be hard to tell apart since they differ drastically from their canonical forms.
Even in your example, ง
looks like a mirrored C
, while อ
looks like O
.
Doug Cooper has written an interesting article called "How do Thais Tell Letters Apart?" (PDF)
The question Deciphering a handwritten script also has a great answer by a person whose profession is reading manuscripts; in their answer, they describe some practical techniques for recognizing symbols in a handwritten text.
Further reading
- Language recognition chart on Wikipedia.
- If you speak Russian, there's a great book, „World language identification by script“ (1961) written by Gilyarevsky et al (Гиляревский, Гривнин — «Определитель языков мира по письменностям») available online (landing page)
P.S. Your sample is in Thai, and the inscription says, อย่างนี้ตลอดไป รักเสมอ, "{wish it to be} forever this way, an eternal love". Also, it's a pretty common tradition in Thailand to attach one's dreams and wishes to a ballon or a floating basket and let it fly/float.
P.P.S. Language identification question by itself are offtopic, since they do not help further visitors. However, questions on methodology of language identification seem to be quite on topic. See this Meta question.