Here are my corrections, along with some comments.
1. Thailand has many interesting places. [or] There are many interesting places in Thailand.
2. Travel in Bangkok is very convenient and comfortable. [“Convenient” often means that it saves time, while “comfortable” refers to the feeling you get, like when you sit in a comfortable chair. I am not sure if I agree with this statement or not – isn’t it a bit misleading?]
3. Trat is in the East of Thailand. [or] Trat is in the eastern region of Thailand.
4. Lampang Province is located about 600 km away from Bangkok. [We don’t use the word “far” when giving the precise distance like this.]
5. People are kind, friendly and warm-hearted. [Spelling!]
6. Thais are always really friendly, whether you buy what they are selling or not.
7. The lifestyle here is quite tranquil. People are very friendly and always have smiles on their faces [or] always keep smiling. [We often use “according to” to report what someone else said: “According to my friend, Khao San Road is a fun place to stay.”]
8. Ko Kret is also one of the destinations in Nonthaburi which you shouldn’t miss.
Note: It’s easy to mix up “where” and “which” relative pronouns. If you can make the relative clause into a separate sentence with “there” in place of the relative pronoun, use where, otherwise we often need which instead. For example:
Thonburi is part of Bangkok. I live THERE. > Thonburi is the part of Bangkok WHERE I live.
9. Pattaya is a popular place in Chonburi which many tourists would like to visit. [Since with the verb “to visit” we don’t usually use “there”, which is the correct relative pronoun.]
10. You will have good memories when you stay with us. [or] Staying with us will make your trip a memorable one.
A final note: in many cases, the problems we see are connected to the part of speech. Kind (adj.) vs. kindness (noun), convenient (adj.) vs. convenience (noun), memorable (adj.) vs. memory (noun). When you edit it’s useful to focus on parts of speech. Learn to analyze your own writing – for example, try to understand why an adjective rather than a noun is needed in one particular sentence. It’s often possible to restate the same idea just by shifting the parts of speech. This comes in handy when you need to paraphrase your sources and avoid plagiarism!
