Hindi is a widely spoken language in and around India, and, as a result, it's an invaluable tool for communication with just about anyone that you might run into in that part of the world. However, just because the person you run into happens to speak Hindi, doesn't mean that they speak it well. A lot of Hindi speakers do not speak it as a native language (just like you), and so, just like you, they're going to make some mistakes. In fact, some of them make a lot of mistakes. Here, then, is a brief tutorial on how to speak better Hindi by watching out for the things people do that are different or just plain wrong.
First of all, it should be noted that in common usage, gender distinctions on nouns tend to blur somewhat. If it's not obviously female, and you can't remember the noun gender, just assume it's masculine, and if it's not, nobody will really notice. They might be using it wrong, too.
Many speakers will use the pronoun हम instead of मैं for "I" as well as in its normal plural usage as "we." Perceptions on the connotations of using हम vary from place to place, and so your mileage in emulating this practice may vary. If you don't even want to worry about it, always using मैं for "I" and हम for "we" will not cause any problems.
Many people tend to pronounce the "dotted" consonants as their standard equivalents. Native speakers of English (or most other Western languages) won't notice the difference between ग़ and ग, क़ and क, or ख़ and ख. However, the differences between ज़ and ज as well as फ़ and फ probably will stand out. If you hear a strange word with a ज or फ, before you get too confused, think if there may be an equivalent common word with a ज़ or फ़.
In a passive sentence, the doer, marked by "by" in English, is marked by द्वारा or के द्वारा in Hindi. However, there are quite a few speakers who will mistakenly use ने instead. This is wrong, but watch out for it. Misuse of ने is common among non-native
speakers of Hindi.
The use of the postposition pe is not really a mistake, but it is not formal usage either. Its standard equivalent is पर. People will also say ke instead of कर in verbal expressions. However, even in formal use, people will always say करके, probably because करकर sounds odd.
Native speakers of languages like Tamil (or English!) that do not have an aspiration distinction may get confused about how to properly pronounce aspirated consonants. In writing, it gets even worse, with spelling distinctions like त and थ being ignored.
Speaking of bad spelling, chatting online with speakers of Hindi is a great way to practice your skills and to communicate with people if there is nobody in your immediate area to talk to, but keep in mind that a lot of people who frequent chat rooms in any language tend to be lazy about spelling and make frequent use of abbreviations, and this problem is only increased since most Hindi chat on the Internet still goes on in Romanization, in the so-called "Bollywood" system of Romanization, which is not really a system at all but the sounds of Hindi forced into an alphabet which does not have enough symbols to describe them all. The first casualty is the distinction between retroflex and dental consonants, which is almost always lost. Short and long vowels are sometimes marked, and sometimes not. When a long vowel is marked, it always with the English spelling conventions of ee and oo, not ii or uu, for ई and ऊ, respectively. Some take this even further and write the vowel ए as not e but ay. The distinction between aspirated and unaspirated is usually preserved with the letter h,
but, as before, some speakers may write verb endings like -tha, -the, -thi and obliterate that distinction as well.
So don't be afraid to make mistakes, because you're not the only one.