1. Set a goal. You've probably heard of SMART goals: specific, measurable, achievable, realistic, timetabled. How will you know, at the end of the year, if you have "learned Italian"? Difficult to quantify. But how about, this year I will complete all the exercises in "Colloquial Italian", or spend a week in Venice and strike up conversation with five strangers? You will know if you have done those things. You may then find it helpful to break it down into smaller steps.
2. Stay motivated. Yes, right now it's January, and you're feeling enthusiastic, but at some point it may feel harder going. Make a list of five reasons why learning the language you have chosen is a good idea, how it will improve your life. Return to your list when you feeling fed up.
3. Find a tutor. Most of us do not have the discipline to keep up self-study entirely by ourselves, long-term. You don't have to have a lesson every week, if time or funds don't allow it: even knowing that you will have a monthly "check up" and opportunity to ask questions can be enough. A good tutor will be able to advise you on learning materials, too, and activities that suit your learning style. For professionals teachers where you live, check the Language School Teachers website; there are also organizations like Armchair Languages who offer lessons by Skype, with all the added advantages of flexibility that brings.
4. Get a good textbook. Particularly at beginner level, a textbook will be invaluable to you, so that you can lay effective foundations and progress incrementally. For French, you can't do better than the Grammaire Progressive du Francais series, although it's possible you will find it a bit dry without something else to complement it. For a good, well-rounded approach, the Colloquial series is good, and you can buy those in a pack which include CDs, for listening practice.
5. Listen to Podcasts: you are, in all likelihood, busy. You don't have hours and hours to devote to this new endeavour. But you do, probably, sit in traffic or stand, squashed, on public transport for a substantial proportion of your week. Use the time to listen to one of the many podcasts available, like the Coffee Break series.
6. Read Books: At every stage of language learning, there are books that can work for you, help you to see how the grammar works for you. A good language bookshop such as Grant and Cutler will be able to advise you on Easy Readers, which are a series of simplifed, abbreviated novels especially designed for learners at various stages. as you progress, you might want to move on to children or young people's fiction, or to translations of classics that you know well already.
7. Read Magazines. As adults, we filter out enormous quantities of information that is not immediately relevant to us. But if we read something that is related to a topic of interest, we are more likely to remember it. If you are intermediate or above (B2+), browse the press shops next time you are on holiday and consider subscribing to a magazine in a topic that interests you. (Ask your tutor or your language bookshop for advice on specialised language learning magazines if you are a beginner, or lower-intermediate.)
8. Watch DVDs. Films and TV series are a great source of vocabulary and idioms, and subtitles are a fantastic resource. At the beginner stage, try watching in your native language (say, English) and read the subtitles in your target language (say, Spanish). Intermediates can watch in Spanish, with subtitles in English, and then finally subtitles in the Spanish, moving on to no subtitles at all. Choose wisely, though: you probably don't want to start with The Wire or The West Wing. Something visual like Friends can work well for this, especially because the episodes are short and the storylines are not too complex.
9. Speak to people! That is, after all, probably the point, isn't it? If you type in "Russian" and "London" to meetup.com, you will find there are at least seven groups that you can join or visit where you will be able to practise your language skills.
10. Exchange emails. Remember Pen Pals, from the days of snail mail? Mylanguageexchange.com helps you to find people with whom you can exchange email, and practise conversation that way.
11. Little and often is the key. Websites like Transparent.com will email or tweet you a new word or phrase each day in the language of your choice. (For those of us who still like using paper, you can also buy physical calendars.)
Then come back and let us know you get on!